Preheat oven to 400F. Dice onion and add to sauté pan with olive oil, garlic powder, red pepper flakes, and salt over medium heat. Cook until glossy and soft.
Add sausage to the pan with cooked onions.
Cook sausage until browned.
Transfer onions and sausage to a plate lined with paper towels to drain the excess fat.
Combine cooked sausage with minced parsley and toss together.
Roll out the puff pastry sheet and cut into 6 squares. Transfer to parchment-lined baking sheet.
Divide the sausage mix among the 6 squares.
Divide the shredded cheddar cheese among the 6 sections of puff pastry.
Pinch them closed by joining corners until they are fully closed.
Brush each with milk and bake for 20-23 minutes. You can place a square of tinfoil on top of each pie, if needed, to keep them from burning.
