In the bowl of a stand mixer, combine milk and yeast and let stand for 5 minutes. Add flour, 2 1/2 teaspoons salt, 5 tablespoons butter pieces, and sugar. With dough hook, mix on low until mixture just comes together. Increase to medium-high; beat until butter is incorporated and dough is soft, 10 minutes.⏱ 15 min
Lightly coat a large bowl with cooking spray. Form dough into a ball, place in bowl, and cover with a damp clean dish towel. Set aside in a warm, draft-free place and let rise until dough doubles in size, 1 to 2 hours (or refrigerate overnight; bring to room temperature before baking).⏱ 120 min
Lightly coat a 9-by-13-inch rimmed baking pan with cooking spray. Turn dough out onto a work surface and loosely cover with damp towel so it doesn't dry out. With a sharp knife, divide dough into 24 pieces, roll into smooth balls (about 2 inches each), and arrange in pan, 1/2 inch apart. Cover with towel and let rise until rolls begin to touch, 1 to 2 hours.⏱ 120 min
Preheat oven to 350 degrees. Brush rolls with half the melted butter; bake until golden brown, 30 minutes. Brush with remaining melted butter, sprinkle with salt, and serve warm.⏱ 30 min