Mix. Combine the warm milk, yeast, sugar, egg and yolk in a stand mixer. Add 31/4 cups flour and the salt, mix to a shaggy dough, then add the softened butter and knead 8 minutes, until smooth and tacky. Add flour a tablespoon at a time only if it will not clear the bowl.

First rise. Cover and rise in a warm place 60 to 90 minutes, until doubled.

Shape. Divide into 15 pieces (about 55g each), roll each into a tight ball, and arrange in a buttered 9x13 pan in a 3x5 grid.

Second rise, or hold. Rise 45 to 60 minutes until puffy and touching, then bake. Or cover tightly and refrigerate overnight, or freeze (see below).

Bake. 375°F (190°C) for 18 to 22 minutes, until deep golden and the center roll reads 190°F.

Butter. Brush the hot rolls generously with melted butter and sprinkle with flaky salt.