Irish Boxty Potatoes

INGREDIENTS

• 2 pounds russet, Yukon gold, or long white potatoes, peeled
• Coarse salt and freshly ground black pepper
• 1 cup milk or cream
• 4 tablespoons unsalted butter
• 1 cup grated russet potato, squeezed dry to remove excess moisture
• 1 large egg
• 1 large egg yolk
• 1/4 cup milk
• 1/4 cup thinly sliced scallions
• 1/2 cup all-purpose flour
• 2 teaspoons coarse salt
• 1 teaspoon baking powder
• 1/2 teaspoon freshly ground pepper
• 1/4 cup unsalted butter, preferably Irish, plus more for serving