In a large bowl, mix the warm milk and yeast. Cover and let sit for 15 minutes.

Add the remaining dough ingredients, adding the flour last and gradually, mixing as you go.

Divide the dough in half.

Line a baking pan with parchment paper and brush it with olive oil.

Dust your work surface with flour and roll out half the dough into a thin sheet.

👉 How thin you roll the dough depends on the size of the pan you want to cover.

Transfer the rolled-out dough to the pan.

Add all the filling ingredients: the cheeses, mushrooms, heavy cream, black pepper, and thyme.

Dust the work surface with flour again and roll out the remaining dough.

Cover the pie with this sheet and seal the edges well so the filling doesn't leak out.

Brush the top with the egg yolk.

Scatter the butter pieces on top and sprinkle with sesame seeds.

After removing from the oven, let it cool before cutting so the filling sets.

👉 Alternatively, you can use only kasseri cheese, make half the amount of dough, and roll out just one sheet. Roll it up, then shape it into a spiral or bake as is.
(Still brush with egg yolk and add the toppings as above.)