In a large metal baking pan (I don't have measurements- approximate at about 15x12-inch and anything close), layer 1/2 of phyllo sheets, brushing each one generously with butter before adding next, and staggering across pan to get all corners covered.
Combine cheeses well and place in pan.
Spread out evenly.
Cover with remaining phyllo sheets, brushing each one generously with butter before adding next, and staggering across pan to get all corners covered.
Tuck in loose edges and brush top of pastry generously with more butter.
With the tip of a pointy knife, mark lines where you'll eventually want to cut the pieces once baked.
These act as steam vents.
Make sure you don't cut all the way into bottom layer of pastry- you just want to cut through the top layer.
Pour over any remaining butter.
Combine milk with the eggs and beat well.
Pour over pastry and allow to sit, at room temperature for 30 minutes to absorb the custard.
Preheat oven to 375°F (190°C).
After 20 minutes, place pastry in oven and bake till golden-brown on top.
For the last 10 minutes of baking, place pan on floor of oven to ensure a crisp, properly-baked bottom crust.
Allow to cool for at least 15 minutes before cutting pieces.