In a large saute pan, heat 2 tablespoons oil over medium heat. Add onions, season with salt and pepper, and cook, stirring occasionally, until translucent. Reduce heat to low and continue cooking, stirring occasionally, until onions are golden, 30 to 40 minutes. Set aside.

Meanwhile, cook bacon in a second large saute pan over medium heat until it begins to crisp but still has some fat. Let cool. Cut into 3-inch strips. Set aside. Mix fromage blanc, mascarpone, and creme fraiche together with the flour. Season with salt and pepper as needed. Set aside.

Preheat oven and pizza stone to 500 degrees F. Using plenty of flour, roll a ball of dough into a 10- to 11-inch circle. Pinch crust slightly around the edge to form a rim. Sprinkle pizza peel with cornmeal and transfer dough to peel. Dimple the dough with your fingertips, then brush 1 teaspoon olive oil over the dough, leaving a ½-inch border.

Spread one-quarter of the cheese mixture over the dough, then one-quarter of the onions. Distribute one-quarter of the bacon pieces on top. Slide the tarte onto the pizza stone and bake 12 to 15 minutes, or until the cheese bubbles and the crust is a deep golden brown. Remove the tarte from the oven with the peel; cut into slices. Repeat process with remaining tartes.