Proof the yeast: In a small Mixing Bowl or Measuring Cups, combine the warm water (105–110°F), 2 ¼ tsp levadura seca activa un paquete estándar, and 1 tsp 1 tsp azúcar granulada para activar la levadura. Stir gently and let sit for 5–10 minutes until foamy and fragrant. If it doesn't foam, your 2 ¼ tsp levadura seca activa un paquete estándar may be expired or the ¼ cup agua tibia 105–110°F was too hot — start over.

In the bowl of a Stand Mixer (or a large Mixing Bowl), whisk together the warm 1 cup leche entera calentada a 105–110°F, 4 tbsp mantequilla sin sal derretida y ligeramente enfriada, más para engrasar melted, 2 tbsp 1 tsp azúcar granulada para activar la levadura, 1 ½ tsp sal fina, and beaten 1 egg a temperatura ambiente, ligeramente batido. Pour in the proofed 2 ¼ tsp levadura seca activa un paquete estándar mixture and stir to combine.

Add 3 cups of the 3 ½ cups harina de trigo común más para espolvorear and mix with the dough hook on low speed until a shaggy dough forms, about 2 minutes. Increase to medium speed and knead for 6–8 minutes, adding the remaining 3 ½ cups harina de trigo común más para espolvorear a tablespoon at a time, until the dough is smooth, elastic, and just slightly tacky — it should pull away cleanly from the sides of the Mixing Bowl but not be stiff or dry.

Shape the dough into a ball and place it in a lightly 4 tbsp mantequilla sin sal derretida y ligeramente enfriada, más para engrasar-ed large Mixing Bowl. Turn to coat all sides. Cover with a clean kitchen towel or Plastic Wrap and let rise in a warm, draft-free spot until doubled in size, about 1 hour.

Grease a 9×13-inch Baking Dish with 4 tbsp mantequilla sin sal derretida y ligeramente enfriada, más para engrasar. Punch down the risen dough and turn it out onto a lightly 3 ½ cups harina de trigo común más para espolvorear-ed surface. Divide the dough into 12 equal pieces (a Bench Scraper or Kitchen Scale helps). Roll each piece into a smooth ball by cupping your hand over it and rolling in a circular motion against the counter.

Arrange the dough balls in the prepared Baking Dish in a 3×4 grid, leaving a little space between each. Cover loosely and let rise again in a warm spot for 30–45 minutes, until the rolls are puffed and touching each other.

Preheat your Oven to 375°F while the rolls complete their second rise.

Bake the rolls for 18–22 minutes, until the tops are deep golden brown and the internal temperature reads 190°F. Rotate the pan halfway through baking for even browning.

Remove from the Oven and immediately brush the tops generously with the 4 tbsp mantequilla sin sal derretida y ligeramente enfriada, más para engrasar melted. Let cool in the pan for 5 minutes, then serve warm.