Potato Irish Champ

Ingredients

• 5 large potatoes ((about 3 lbs or 1.5 kg), peeled, halved lengthwise and cut into 1-inch chunks)
• 1 cup 2% milk (plus 2 tablespoons)
• 1 bunch scallions ((6-8 scallions), washed, trimmed and thinly sliced)
• 1 tsp kosher salt
• 1/8 tsp ground black pepper
• 4 tbsp butter (melted)