Combine milk, flour, yolk, cream cheese and 50 g of cheese in a pot, beating with electric mixer. Sprinkle in salt and white pepper and bring mixture to boil on medium heat, stirring often. Mixture will be thickening.
Take off from heat and let cool to room temperature, completely
Once mixture is cooled, beat in left over butter and another 50 g of grated cheese.
Pour filling into a piping bag of ziplock bag, snipped the corner
Pipe some filling into shells and give some leftover cheese, the pipe some more filling, then top the filling with cheese again