Mini Quiche Lorraine

Preheat the oven to 375 degrees F (190 degrees C). Arrange tart shells in two 12-cup muffin tins; line each shell with a layer of pie weights or dried beans.

Bake in the preheated oven until crust edges are lightly browned and shells are about 3/4 fully cooked, 5 to 10 minutes. Remove from the oven and let sit until needed.

While the shells are baking, cook bacon in a large skillet over medium-high heat, turning occasionally, until browned and crispy, 7 to 10 minutes. Drain on paper towels and crumble when cooled.

Mix 1 cup Swiss, green onions, and crumbled bacon together in a bowl; divide mixture evenly among tart shells.

Whisk milk, eggs, mustard, salt, and pepper together in a bowl. Ladle egg mixture into each tart shell until about 2/3 full. Sprinkle remaining 1/4 cup Swiss over tarts.

Bake in the preheated oven until set in the middle and shells are golden brown, 25 to 30 minutes.