In a large mixing bowl, with an electric mixer, beat butter and cream cheese until well blended. Add flour, and beat well. Form into a ball and wrap in plastic wrap. Chill in refrigerator for 1 hour.
Shape dough into 24 1-inch balls; place each ball in an ungreased mini muffin pan. Press dough onto bottom and sides. Chill 30 minutes in refrigerator.
In a medium skillet, over medium heat, heat olive oil and butter. Add onion slices and sauté several minutes until brown and caramelized. Remove to a cutting board to cool. Finely chop.
Combine eggs, milk, salt, pepper and garlic powder. Preheat oven to 400 degrees
Evenly divide onion and cheese amongst quiche cups. Spoon 2 teaspoons of egg mixture into each cup.
Bake at 400 degrees for 18-20 minutes, or until lightly browned. Cool pans 4-5 minutes before turning out onto wire rack. Serve warm or at room temperature.
To freeze, cool quiche completely and store in an airtight container. Quiche will keep in refrigerator for 2-3 days; freeze for up to 3 months.