Preheat oven to 400 degrees.
Separate puff pastry shells and arrange on ungreased baking sheet. If desired, line with parchment paper. Bake according to instructions on back of package. I reduced oven temp to 400 (package suggests 425 degrees) for even baking in my oven. Adjust your oven temp if necessary.
While pastry shells are baking, prepare scrambled eggs and cheese.
In medium sized bowl, thoroughly combine 3 eggs, shredded cheddar cheese, milk (whole or 2%), salt and black pepper to taste. Set aside.
Place 1/2 tablespoon of vegetable oil (or olive oil) in a medium sized skillet. Warm over "low" heat until hot.
Pour egg mixture into hot greased skillet. Increase heat to medium. Use a rubber spatula to turn eggs and cheese for 2-3 minutes. "Scramble" by breaking into small pieces with spatula. Cook 2 minutes longer if hard scrambled eggs are preferred.
Remove from heat. Set aside.
Remove baked puff pastry shells from oven. Set aside to cool for 5 minutes. Carefully remove tops which will come out easily.
Fill each shell with scrambled cheese and eggs. Serve immediately.