Preheat oven to 375°F and line a baking sheet with parchment paper.
In a bowl, mix spinach, feta, mozzarella, garlic, olive oil, and black pepper.
Lay out one sheet of phyllo, brush lightly with melted butter, and top with another sheet. Repeat until you have 4 layers.
Spoon spinach mixture evenly across, fold edges, and roll into a log or cut into squares.
Place on baking sheet, brush tops with more butter, and bake 18–20 minutes until golden and crisp.
Cool slightly before serving so you don’t burn your tongue (trust me on this one).