I made this very simple hors d'oeuvre/appetizer for my 2010 Xmas Eve dinner and I think it was my favorite dish of the evening. It couldn't be simpler: just some caramelized onions and blue cheese on puff pastry - but boy, is it delicious. I plan to make it as often as I can!
The original recipe called for making your own bready dough, but I was running late with all Christmas dinner preparations and decided to use up the extra puff pastry I had around instead. It worked out perfectly, though I had to increase the cooking time from that of the original recipe for the pastry to be fully cooked. If you roll the pastry thinner, it'll cook quicker, however. These squares are pretty messy, so make sure to serve them with napkins.
The puff pastry I used is the one that Trader Joe's sells under its own name, which comes in two thick flat sheets. It's pretty good and I think only $4 for a $1 package. The blue cheese was Rosenborg Danish Blue, which I got for $4 lb!!!! @ Grocery Outlet. It's a delicious cheese @ an incredible price.
Blue Cheese and Caramelized-Onion Squares
Melt butter with oil in a large pot over medium-high heat. Add onions and cook until they start to brown and become soft, about 10 minutes. Stir frequently. Stir in the rosemary, sugar and salt. Reduce heat to medium and cook until the onions are soft and dark brown, about 20 minutes, stirring frequently. Let cool.
Preheat oven to 425F
Grease a large baking sheet.
Roll puff pastry sheets on a flour surface until they have the thickness you desire. Transfer to baking sheet and cover with caramelized onions. Sprinkle crumbled blue cheese on top.
Bake in oven until crust is golden and the cheese is bubbling - 20 to 30 minutes. Cut into squares and serve.