Heat an oven to 500° with a pizza stone positioned on center rack. Mix crème fraîche, fromage blanc, nutmeg, and salt and white pepper in a bowl. Set aside.
Whisk flour, baking powder, and 1 tsp. salt in a bowl; make a well in the center. Whisk oil, yolks, and 1⁄2 cup water in another bowl, and pour into well.
Using a fork, stir until a loose dough forms. Turn out onto lightly floured surface; knead dough for 1 minute.
Divide dough into 3 pieces. Working with 1 piece of dough at a time, roll into a 12" circle, and place on a parchment paper—lined baking sheet.
Spread 1⁄2 cup cheese mixture over circle, leaving a 1⁄2" border around edge. Sprinkle with a little of the bacon and onions.
Transfer dough (on parchment paper) to pizza stone. Bake until lightly browned and crispy, 8–10 minutes. Repeat.