Generously grease a 9x13-inch baking pan with some of the melted butter. Preheat oven to 350 degrees Fahrenheit.
Loosely ruffle one by one phyllo dough sheet by pulling the short ends together. There’s no wrong way of doing it. It’s similar to crumpling the paper but instead of crumpling it into a ball you scrunch it along the long side. Work quickly as the delicate sheets dry out fast, or keep the rest covered while you’re ruffling. Place upright into prepared pan. Repeat process with remaining sheets, layering them closely next to each other.
With a pastry brush, brush remaining butter all over your ruffles. Bake until golden brown, about 30 minutes.
In the meantime, heat the milk or cream until just begins to boil. Set aside. Beat together the eggs and sugar in a medium bowl. Gradually add heated milk, a little bit at a time, whisking constantly; add vanilla.
Spoon the milk mixture evenly all over baked phyllo. Toss fruit over the ruffles or create a pattern. Bake until filling has set, 25 to 30 minutes more. Dust with powdered sugar and add more fruit if desired.
For a different flavor, omit the lemon and berries and dust the pie with cinnamon instead.