How to Make It
Preheat the oven to 400°. In a large skillet, cook the bacon over moderate heat until crisp, about 6 minutes. Pour off all but 1 tablespoon of the fat in the skillet. Add the onion to the bacon. Cook, stirring occasionally, until softened, about 8 minutes. Add the thyme and crushed red pepper and let cool.
In a bowl, mix the ricotta with the Parmigiano-Reggiano, garlic and the 2 egg yolks and season with salt.
Cut the puff pastry into 2 rectangles. On a lightly floured work surface, roll out each piece to a 13-by-8 1/2-inch rectangle, about 1/8 inch thick. Place each rectangle on a parchment paper-lined baking sheets. Refrigerate until firm, about 10 minutes.
Using a small knife, score a 1/2-inch border around each rectangle, cutting halfway through the pastry. Brush the borders with the egg wash. Spread the ricotta mixture over each rectangle. Scatter the Gruyère and the bacon-onion mixture on top. Bake in the upper and lower thirds of the oven for about 20 minutes, until the pastry is richly browned; switch the pans halfway through baking. If the pastry bubbles, poke it with a knife and continue baking.
In a large bowl, whisk the oils with the lemon juice and season with salt and pepper. Add the radicchio and parsley and toss well.
Cut the tarts into squares. Top with the salad and serve right away.