How to Make It
Brush 18 cups of 2 standard-size muffin pans with melted butter. In a small bowl, whisk the warm water with the sugar and yeast and let stand until foamy, about 5 minutes.
In a large bowl, whisk the flour, baking powder and salt. Using your fingers, pinch the cold butter into the flour until the mixture resembles coarse crumbs with some pea-size pieces of butter remaining. Stir in the yeast mixture until the dough is evenly moistened (it will be shaggy), then stir in the yogurt to form a sticky dough. Scoop 1/4 cup of the dough into each buttered muffin cup and let stand in a warm place until risen, about 1 hour.
Preheat the oven to 400°. Brush the rolls with melted butter and stick a rosemary sprig in each one. Bake the rolls in the lower and upper thirds of the oven for 18 to 20 minutes, until golden; shift the pans from top to bottom and front to back halfway through baking. Transfer the rolls to a platter or basket and serve warm.