Preheat the oven to 400 degrees. In a sauce pan, start by melting the butter over medium heat, then add in the onions & saute until translucent. Add in the garlic and mushrooms (I used button - you can use your favorite), and cook until the mushrooms are completely cooked.

After the mushroom mixture is cooked, set aside to slightly cool.

Next, in a mixing bowl, mix together the egg & ricotta cheese.

Squeeze the moisture out of the spinach using a kitchen towel, then add it to the ricotta mixture & incorporate them together. Add in the mushroom mixture & both kinds of cheese, salt & pepper - mix all together to create the filling.

Using thawed puff pastry dough (the kind from the freezer section), open up a whole sheet, then take 1/3 of another sheet and seal the edges with your fingers on a lightly oiled 9 x 12 sheet pan (or just center it on a larger pan.) Prick the dough all over with a fork to keep it from rising too much in the middle.

Put the filling on top, spreading it out over the dough, leaving about a 1/2 inch rim around the edge. Bake at 400 degrees for 20-25 minutes or until edges are lightly brown.