Special equipment: a 12-cup muffin tin
Grease a 12-cup muffin tin with butter.
Put the yeast in a small bowl. Add 1/2 cup warm water and let stand until foamy, 5 minutes.
Combine the cake flour, sugar, baking powder and salt in a large bowl, and whisk to combine. Add the proofed yeast, milk, egg and melted butter; whisk to combine.
Divide the batter evenly among the prepared muffin cups. Let stand at room temperature until slightly risen, 30 to 40 minutes.
Meanwhile, preheat the oven to 400 degrees F.
Bake the rolls until golden all over, 20 to 25 minutes. Serve warm.