Heat the oil in a medium skillet over medium-low heat until it shimmers. Add the onion and a pinch of salt and cook, stirring occasionally, until very soft and golden, about 15 minutes. Set aside.

Preheat the oven to 375 F. Spray nonstick 24-cup mini muffin tin with cooking spray.

Meanwhile use a 2 1/2 round cutter to cut out 24 rounds from pie crust. Fit the rounds in the cups of muffin tin, pushing the bottoms down and pleating the sides slightly.

Whisk the half-and-half, egg and egg yolk, cayenne and some salt and pepper together in a medium bowl until very well combined. Stir in the chives and transfer to a liquid measuring cup. Divide the onions and ham evenly among the 24 dough-lined muffin cups. Divide the half-and-half mixture evenly among the cups.

Bake until quiches are puffed and golden, about 20 minutes. Let cool in the muffin tin about 5 minutes, then remove to a wire rack. Serve slightly warm or at room temperature.

For the Mini Bacon Quiche: 3 ounces Swiss cheese grated 3 slices bacon fried and crumbled 2 tablespoons green onion sliced For the Mini Ham and Cheese Quiche: 3 ounces Swiss cheese grated 1/4 cup (about 1.5 ounces) ham cubed For the Mini Spinach Quiche: 3 ounces Swiss cheese grated 4 cups (3 ounces) spinach wilted (see notes) 1 tablespoon red bell pepper cubed For the Mini Mushroom Quiche: 2 tablespoons (1/2 ounce) mushrooms finely chopped 3 ounces Swiss cheese grated