Place the 3 lb papas Yukon Gold peladas y cortadas en trozos de 1½ pulgadas chunks in a large Pot and cover with cold water by at least 1 inch. Add a generous pinch of 8 tbsp mantequilla sin sal cortada en porciones de cucharada, tibia a temperatura ambiente (about 1 tbsp). Starting in cold water ensures the potatoes cook evenly all the way through.

Bring the Pot to a boil over high heat, then reduce to a steady simmer. Cook the 3 lb papas Yukon Gold peladas y cortadas en trozos de 1½ pulgadas until completely tender — a fork or Knife should slide in and out with zero resistance, about 18–22 minutes. Don't rush this step; undercooked potatoes make lumpy mash.

While the 3 lb papas Yukon Gold peladas y cortadas en trozos de 1½ pulgadas cook, warm the ¾ cup crema pesada tibia and ¼ cup leche entera tibia together in a small Saucepan over low heat, or microwave in a heatproof cup for about 60 seconds until steaming. Keep warm. Cold dairy added to potatoes will make them gluey and dense.

Drain the 3 lb papas Yukon Gold peladas y cortadas en trozos de 1½ pulgadas thoroughly in a Colander and return them to the hot Pot over low heat. Shake the pot gently for 1–2 minutes to evaporate any remaining moisture — this is key for fluffy, non-watery mash.

Pass the 3 lb papas Yukon Gold peladas y cortadas en trozos de 1½ pulgadas through a ricer or Food Processor directly back into the Pot for the silkiest result. Alternatively, use a Potato Masher for a more rustic, slightly textured mash. Avoid using a Hand Mixer or Blender — overworking the starch makes potatoes gluey.

Add the room-temperature 8 tbsp mantequilla sin sal cortada en porciones de cucharada, tibia a temperatura ambiente pats a few at a time, folding them in gently with a Spatula or Wooden Spoon after each addition. Let each addition melt fully before adding the next. Adding butter before the cream gives you a richer, more emulsified result.

Pour in the warm ¾ cup crema pesada tibia and ¼ cup leche entera tibia mixture gradually, folding it in until the 3 lb papas Yukon Gold peladas y cortadas en trozos de 1½ pulgadas reach your desired consistency. You may not need all of it, or you may want a splash more ¼ cup leche entera tibia for a looser mash — adjust to your preference.

Season with 1½ teaspoons of 1 ½ tsp sal kosher más para el agua hirviendo and the ¼ tsp pimienta blanca molida recientemente; o sustituir con pimienta negra. Taste and adjust — potatoes need more salt than you think. Fold gently to combine.

Transfer to a warm serving Mixing Bowl. Make a shallow well in the center and pour in the optional melted 8 tbsp mantequilla sin sal cortada en porciones de cucharada, tibia a temperatura ambiente. Garnish with fresh 2 tbsp cebolletas frescas cortadas finamente if desired. Serve immediately.