Preheat oven to 375 degrees.
Lightly spray a 13x9 inch baking dish with cooking spray.
In a blender or food processor, puree the cheese until very smooth. Add butter, ½ teaspoon pepper and salt…. Note if you are using feta, use less salt.
Start laying your potatoes in the lightly greased pan and top with one third of the cheese mixture.
Repeat with another layer of potatoes and cheese,
Repeat one more time with one more layer and the last 1/3 of the cheese mixture
Place pan on a cookie sheet to catch any drips.
Cover the pan tightly with foil and bake until potatoes are tender, 1 to 1 ½ hours.
In a medium bowl, whisk together the eggs, yogurt and ¼ teaspoon of pepper.
Pour over the potatoes and bake uncovered until the custard is puffy, golden and set. About 20 minutes or more.
Let cool 5- 10 minutes before serving.