Preheat oven to 400 degrees F (200 degrees C). Grease and flour a 12-cup muffin tin.

Line the muffin cups with the 12 pastry rounds.

Heat 2 tablespoons butter in a skillet over medium heat; cook and stir green onions until tender, 3 to 5 minutes. Add corn, salt, pepper, and nutmeg; cook and stir until heated through, about 2 minutes. Remove skillet from heat.

Heat 3 tablespoons butter in a saucepan over medium heat; add flour and cook, stirring with a wooden spoon, until a paste forms, about 1 minute. Slowly pour in milk, whisking constantly, and cook until a thick sauce forms and starts to bubble, 2 to 3 minutes. Add half of the Parmesan cheese and stir until smooth; remove from heat. Stir sauce into corn mixture.

Fill pastry with corn mixture and top each with remaining Parmesan cheese.

Bake in the preheated oven until golden, about 15 minutes.