Prep the Crust
Preheat oven to 375°F (190°C). Spray a 12-cup standard muffin tin generously with non-stick spray.
Let refrigerated pie crust sit at room temperature 15–20 minutes until pliable.
On a lightly floured surface, unroll the dough. Use a round cookie cutter slightly larger than the muffin cup opening (about 3½–4 inches) to cut out circles.
Press each dough circle into a muffin cup, gently pressing it into the base and up the sides. Keep the dough cold — colder dough makes a flakier crust.
Blind Bake the Crust (Optional but Recommended)
Line each dough cup with a small piece of parchment; fill with pie weights or dry beans.
Bake 15 minutes until edges are lightly set. Remove parchment and weights.
Bake 5–8 more minutes until the bottoms are dry and just barely golden. Remove and let cool slightly.
Prepare the Fillings
Bacon: Fry bacon until crisp; drain on paper towels and crumble. Sauté diced onion in the same pan until soft.
Spinach: Heat a drizzle of olive oil over medium heat; add garlic and spinach; sauté 1–2 minutes until fully wilted. Squeeze out all excess moisture in a paper towel before using.
Mushrooms: Melt butter in a pan over medium-high heat; add mushrooms; cook undisturbed until deeply golden, about 4–5 minutes. Add garlic and thyme; cook 1 minute more.
Make the Egg Custard
In a medium bowl or 4-cup measuring cup, whisk eggs, milk, heavy cream, salt, pepper, and nutmeg until smooth and slightly frothy — about 1 minute of vigorous whisking. The measuring cup spout makes pouring into cups much neater.
Assemble and Bake
Distribute your chosen fillings evenly into the pastry shells — cheese and fillings go in first.
Pour the egg custard slowly over the fillings, filling each cup about ¾ full. Leave space for the custard to puff up during baking.
Bake 25–30 minutes until the tops are puffed, golden brown, and the centers are just set. A toothpick inserted in the center should come out clean.
Let cool in the muffin tin 5 minutes before removing. Run a thin spatula around the edges and lift out carefully.
Crustless Mini Quiche (Egg Muffin Style)
Skip the pastry completely. Spray the muffin tin very generously. Add fillings directly to the greased cups, pour egg custard over top, filling ¾ full. Bake at 375°F for 20–25 minutes until set and golden on top. Cool 5 minutes before removing — these are more delicate, so give them time to firm up.