Let Me Tell You About This Tart (And My Cat… Briefly)

Honestly, this caramelized onion tart with gorgonzola and brie is one of those things that got me through last year’s long winter. The first time I made it, I almost set off the smoke alarm because, turns out, onions take way longer to caramelize than any recipe online claims. My cat, Pickles, was more interested in sniffing the brie than the onions, which is saying something because she usually makes a beeline for anything remotely fishy. Anyway, this tart? It became my dinner-party go-to, and even my picky cousin—who claims he ‘doesn’t do blue cheese‘—polished off two slices.

Why I Keep Coming Back to This Tart

I whip this up when I’ve got friends coming round, especially if I’m tired of the same old cheese platter. My family goes crazy for the oozy brie and tangy gorgonzola combo—once, I tried using only cheddar (I’d run out of both blue cheese and brie), and, well, everyone immediately noticed. The crust is buttery but honestly, store-bought puff pastry is perfectly fine (no need to wrestle with flour everywhere). Plus, if you’re anything like me, this tart can forgive a little impatience—burnt onions? Slice off the worst bits; pile on more cheese!

Here’s What You’ll Need (And What You Can Swap)

2 large onions (yellow or red; sometimes I use a mix if that’s all I have left—granny always insisted on yellow, but she also boiled carrots until they disintegrated so…)
2 tablespoons butter (or olive oil in a pinch—honestly, both work just fine)
1 sheet puff pastry (store-bought, cold; homemade if you’re feeling like a champion, but supermarket is my lifesaver)
100g brie cheese (rind on or off—it melts anyway, so I usually get lazy and leave it)
80g gorgonzola (any blue cheese works—stilton, Danish blue, even Roquefort if you’re feeling fancy)
1 teaspoon fresh thyme (dried is OK, about 1/2 teaspoon)
1 egg (for brushing; but sometimes I skip this because who has just one egg lying around?)
Salt and black pepper
Optional: a sprinkle of walnuts or pecans; a drizzle of honey (nice, but I usually forget)

How I Actually Make This Tart (Warts and All)

Get your onions going. Slice the onions thin(ish)—not so thin you’re crying for an hour, but not chunky. Throw them in a big pan with the butter over low heat; stir now and then, but you can honestly leave them alone while you scroll through social media for a bit. It’ll take 25–30 minutes (not eight, like some recipes claim!). They’ll go all golden and sticky. If they start getting too dark, add a splash of water and give it a stir. This is where I usually sneak a taste and hope no one notices.
Get the oven hot. Crank it to 200°C (that’s 400°F for those of you not on the metric bandwagon). Line a baking tray with parchment. Or foil. Or just butter it—it all works.
Shape the pastry. Roll out the puff pastry so it’s roughly the size of a small baking sheet. Sometimes mine is a bit lopsided. That’s okay, we’re calling it “rustic.”
Layer on the onions. Plonk the onions all over, leaving a bit of a border (maybe an inch). If you don’t, the cheese escapes; learned that one the hard way.
Add the cheese. Dot with chunks of brie and gorgonzola. Don’t fuss—an uneven cheese distribution just means some bites are cheesier. Scatter thyme on top, some black pepper, and salt if you want. Sometimes a few nuts or honey, if you’re feeling it.
Crimp the edges. Fold them over so you get a little crust. Brush with beaten egg if you remembered to keep one aside. If not, milk or nothing still works just fine.
Bake! 20–25 min, until golden and puffed and you cannot stand the smell any longer.
Let it cool a minute. This is the hardest part. But, actually, if you cut into it too early, the cheese just runs everywhere. Trust me.

Notes from My Chaotic Kitchen

I once made this with red onions and forgot the thyme—honestly, it was still gorgeous.
If your pastry leaks cheese, scrape up the crispy bits from the tray—arguably the best part.
Brie rind: I used to be religious about removing it, but now I leave it. No one’s complained.

Some Variations I’ve Tried (And a Miss…)

Leeks instead of onions: weirdly sweet, but good!
Added cooked bacon bits for my meat-eating uncle—he asked for seconds. Not that I got any credit.
Mushrooms and onions—well, this made it a bit soggy. Maybe I used too many. Won’t do that again, probably.
Splash of balsamic on the onions? Oh yes, game changer.

Stuff You’ll Need (And a Cheat if You Don’t Have It)

Baking tray (I’ve used a pizza stone in a pinch—sort of worked)
Parchment paper (or foil, or just butter your tray if you run out—it’ll survive)
Sharp knife (unless you’re one of those people who tear cheese by hand. Respect.)
Big frying pan (saucepan is okay if you really pile those onions in, just stir a bit more)

Caramelized Onion Tart with Gorgonzola and Brie

How to Store Leftovers (Like You’ll Have Any…)

Technically, you can wrap leftover slices in foil or store in an airtight container in the fridge. Lasts maybe 2 days—though honestly, in my house it never lasts more than a day! Actually, I’ve found the flavors deepen overnight, but the pastry gets a little soft; still good cold or reheated in the oven (not the microwave, unless you like rubbery cheese).

Here’s How I Like to Serve It

I think it’s a star all by itself, but if you’re feeling posh, toss together a simple salad—just greens, olive oil, and a sprinkle of flaky salt. My friend Emma swears it pairs best with a cold glass of Sauvignon Blanc (linking her favorite here if you’re a wine nerd).

Occasionally, we serve it for brunch with a fried egg on top. Wild, I know.

A Few Pro Tips (Learned the Hard Way…)

I once tried to caramelize onions on high heat. Don’t. It doesn’t save time, just burns them. Low and slow, mate.
Rolling out puff pastry while it’s too warm? Disaster. Keep it cold or it sticks to everything.
Bake on the middle rack. I once put it on the bottom and the pastry burned before the cheese. Oops.

Questions People Actually Ask Me

Can I use gluten-free pastry?
Yes, but—I have to admit the texture is different. Still tasty! My friend Mia uses this brand: Schar if you want to look it up.

Is gorgonzola super strong?
It is, but in a good way. If that’s not your thing, swap for a milder blue or extra brie. Actually, goat cheese works too, but skip if you hate tangy things.

Can I prep ahead?
Sort of! You can defrost pastry and caramelize onions the night before (that’s what I do when I’m trying to look organized). Assemble just before baking though—the filling makes the pastry soggy if it sits too long.

What if I don’t have fresh thyme?
Honestly, dried thyme or even oregano gets the job done. Once I forgot herbs entirely and no one cared.

Before I Forget—A Little Rant

One last thing—don’t stress if it doesn’t look like a fancy bakery tart. It’s home cooking, right? Sometimes my dough’s lumpy, my cheese lands in uneven piles, and I’ve definitely eaten the last piece straight from the fridge at midnight. Honestly, that’s the best way. Happy cooking!