In a large skillet, heat over medium heat and add the bacon strips. Cook for about 6–8 minutes until they are crispy and browned, turning occasionally. Once done, transfer the bacon to a paper towel-lined plate to drain excess fat, leaving about 2 tablespoons of the rendered fat in the skillet for added flavor.

Using the remaining bacon fat in the skillet, add thinly sliced sweet onions. Sprinkle with kosher salt and black pepper, then cook over medium-low heat for 25–30 minutes, stirring often. Add a splash of apple cider, cooking for an additional 5 minutes until the onions are sweet and caramelized, then set aside.

Preheat your oven to 400°F (200°C). While the oven is heating, roll out the frozen puff pastry sheets lightly on a floured surface. Place the rolled pastry onto your baking sheet, scoring a 1-inch border around the edges. Prick the center to prevent puffing during baking.

In a mixing bowl, combine the ricotta cheese with pumpkin purée and season with kosher salt and pepper. Spread this filling evenly over the center of your prepared pastry, leaving the border free. Layer the caramelized onions, crumbled bacon, and shredded mozzarella cheese on top.

Scatter the fresh sage leaves over the top. Lightly beat together an egg and splash of water, then brush this egg wash onto the exposed pastry edges for a golden finish. Bake in your preheated oven for 25–30 minutes until golden brown and puffed.

Once baked, remove from the oven and sprinkle with grated Parmesan cheese. Allow the tart to rest for about 10 minutes before slicing; this makes serving easier.