It could be as easy as just puff pastry with the carmelized onions and gorgonzola. Assuming this is what you’re looking for, I can’t really tell if there’s a sauce in there or not.
If there is a sauce, it sounds enough like the technique for my bacon-onion tarts that I’ll offer this up.
This makes enough filling for 1 9" tart or 4 mini-tarts (I think my mini-tart pans are maybe 2" across?) That’s not a lot, you might want to double it if you want to make a bunch.
I make tart shells using pâte brisée, but you’ll skip that and use the puff pastry. I’d use a mini-cupcake pan and press squares of puff pastry into each cup.
For the filling, first caramelize the onions. If you haven’t done that before, it’s just a matter of slicing them very thin, then cooking them over low heat with some butter & salt until they get brown and sweet. It can take a while, depending on how many you’re cooking. If you need better directions, let me know, or you can google it (it’s a pretty basic technique)
Then, I’d make a quick cream base like so:
1.5 t. flour
1.5 t. butter
~3/4 cup of heavy cream
1 egg, beaten
Melt the butter in a small saucepan over medium-low heat, then whisk in the flour. Continue to whisk for a couple minutes, allowing the flour to lose that raw-flour taste but not burn (if it gets slightly tan that’s fine)
Add the cream in small bits, whisking continuously, until it’s all in there and thickened a bit. Take it off the heat, and stir in the beaten egg.
Add in the Gorgonzola until it tastes sufficiently Gorgonzola-ish to you.
Stir in the caramelized onions. Salt and pepper to taste.
Spoon into the puff pastry shells and cook according to the puff pastry directions until the pastry is done.
