Clarify the butter by melting it in a saucepan over medium-low heat for 10 to 15 minutes. Pour the clarified butter into a bowl, leaving the salt and milk solids behind in the pot.
Preheat the oven to 350 degrees.
Prepare the filling - combine the cream cheese, feta cheese, eggs, onion powder, white pepper and salt in a large bowl and beat with a mixer until combined.
Brush a 9" x 13" baking dish with clarified butter.
Layer 6 sheets of phyllo dough in the baking dish, creating a "parcel" to enclose the fllling, brushing with butter in between each layer. The first sheet is placed off-center to the left, draping over the edge of the pan, the 2nd sheet off-center to the right, the third on the top of the pan, draping over the edge, the 4th on the bottom of the pan and the final 2 layers go in the center of the baking dish.
Pour the filling into the pan.
Fold the sides and top of the phyllo dough over to enclose the filling. Add 6 phyllo sheets to the top, buttering between each layer. Ensure the top layer is fully covered with
Refrigerate the Tiropita for 5-10 minutes to allow the butter to cool and harden, making it easier to cut.
Use a sharp knife to score the Tiropita before baking. You'll want to cut through the top layers of phyllo, but not the bottom layers.
Bake for 40 to 45 minutes at 350 degrees F.
Let the Tiropita cool for 20 minutes before slicing all the way through and serving. Serve warm.