Preheat the oven to 375 degrees F (190 degrees C).
Cook and stir beef and onion in a nonstick skillet until beef is browned, about 5 minutes. Stir in curry powder until heated through and fragrant, 1 to 2 minutes.
Cut puff pastry squares diagonally to create 12 triangles. Fold each triangle in half, pressing the edges of one side together, and leaving an opening for the filling. Fill each triangle with curried beef and press edges to seal.
Coat each triangle with beaten egg using a pastry brush. Arrange triangles on a baking sheet.
Bake in the preheated oven until puffed up and golden brown, 15 to 20 minutes.