Preheat oven to 180° C. Line a baking tray with silicon mat.
Heat butter in a non-stick pan. Add olive oil and button mushrooms and sauté for 1 minute. Add shiitake mushrooms and sauté for 1 minute. Add corn kernels and sauté for 1 minute.
Add spinach, mix and cook for 1 minute. Add cottage cheese, gruyere cheese and processed cheese and mix. Add salt and mix. Add crushed peppercorns and mix well.
Dust the worktop with some flour, place the sheet and roll out into thin rectangle sheet.Cut the sheet into 2 inch squares.
Put some mushroom mixture in the center of each square, brush some water on the edges, fold to make a rectangle and seal the edges. Press the edges with the back of the fork coated with cornflour to create a pattern.
Place the puffs onto the lined baking tray. Place the tray in the preheated oven and bake for 20 minutes.