Combine warm milk, sugar, and yeast in a bowl; let it foam for 5–10 minutes.
Whisk flour and salt in a large mixing bowl.
Stir in the yeast mixture and 5 tbsp melted butter until a shaggy dough forms.
Knead on a lightly floured surface until smooth and elastic, about 8–10 minutes.
Grease a bowl with oil, add dough, cover, and let rise until doubled, 60–75 minutes.
Butter a 9×13-inch baking pan lightly with a little of the melted butter for brushing.
Roll dough to about 1/4 inch thick. Cut 2 1/2-inch rounds, re-rolling scraps as needed.
Brush each round lightly with melted butter, fold in half, and pinch the edge to seal.
Arrange rolls seam-side down in the pan, slightly touching. Cover and proof 25–35 minutes.
Preheat oven to 375°F. Bake until golden, 16–18 minutes.
Brush hot rolls with remaining butter and finish with flaky salt if using. Cool 5 minutes and serve warm.