• 4 slices bacon , cut into 1/2-inch pieces
• 4 small onions , cut in half lengthwise and thickly sliced
• 1 tablespoon plus 1 teaspoon fresh thyme leaves , chopped
• Kosher salt
• 1 cup whole milk ricotta cheese
• 1 egg yolk
• Freshly ground pepper
• 1/4 cup plus 1 tablespoon Parmigiano-Reggiano
• 1 (8-inch) frozen pie or tart shell

Preheat oven to 350°. Cook bacon in a medium frying pan over medium-high heat until fat is mostly rendered and bacon is crisp around edges. Transfer to paper towels to drain, and set aside, leaving 1 tablespoon bacon fat in pan. Crumble bacon after cooling.

Add onions to pan and cook over medium-high heat, stirring occasionally, until they start to brown, about 8 minutes. Turn heat to medium-low and add 1 tablespoon thyme and pinch of salt. Continue to cook until onions are soft and deep golden brown, about 20 minutes more.

Meanwhile, combine ricotta, egg yolk, 1/2 teaspoon salt, pinch of pepper, 1 teaspoon thyme and 1/4 cup Parmigiano in a small bowl. Stir well to combine.

Spread ricotta mixture evenly on the bottom of tart shell. Arrange onions on top of ricotta and sprinkle with 1 tablespoon Parmigiano. Sprinkle bacon over top. Transfer to oven and bake until edges of filling are golden brown, 30 to 40 minutes.