01 -
Turn your oven on to 375°F (190°C).
02 -
First, fry bacon chunks in a big skillet until they're crunchy. Put them aside and keep some of the fat.
03 -
Drop butter into the same skillet with your sliced onions. Cook them over medium heat for 10 minutes, giving them a stir now and then. Turn down the heat and let them cook another 40 minutes until they're brown and sweet. Add some salt and pepper.
04 -
Spread out your dough and fit it into a tart dish. Poke holes in the bottom with a fork and bake it for 15 minutes with baking weights. Take the weights out and bake 5 more minutes till it's got a golden color.
05 -
Layer Gruyère cheese on the bottom of the crust. Pile the browned onions on next. In a bowl, whisk eggs, cream, and thyme together. Pour this mix over the onions.
06 -
Scatter more Gruyère and the bacon bits on top. Stick it in the oven for 25-30 minutes until it's firm and the surface is golden.
07 -
Let your tart sit and cool a bit before you cut into it.