Heat the oven to 180 C / 350 F and line two sheet pans (33 x 46 cm / 13 x 18 inch) with parchment paper.
In a large mixing bowl, whisk together the flour, baking powder, salt, and mahlepi.
Add the oil, warm milk, egg, and sugar. Mix with your hands until a soft dough forms. If it feels dry, add water one tablespoon at a time.
Cover the dough and let it rest at room temperature for 30 minutes.
While the dough rests, make the filling: in a separate bowl, mix the grated halloumi, ricotta, kefalotyri, 4 eggs, semolina, mint, drained raisins, and baking powder until combined.
Divide the dough into 10 pieces, about 85 g each. Roll each piece into a 12 cm / 5-inch round on a lightly floured surface.
Spoon about 3 tablespoons of filling into the center of each round. Fold the sides in to form a square or triangle shape, pinching the edges firmly so the filling shows through the middle.
Place the shaped flaounes on the prepared sheet pans, leaving space between each one.
Brush the tops and edges with the beaten egg, then sprinkle generously with sesame seeds.
Bake for 35 to 40 minutes, until the pastry is deep golden brown and the filling looks set and slightly puffed.
Cool on the pan for 10 minutes before moving to a rack. Serve warm or at room temperature.