Preheat oven to 375°F. Grease the bottom of a 9X12 baking dish with the butter.
Slice the potatoes diagonally in 1/4 – 1/2 inch slices. Leave skins on. Place a layer on the bottom of the dish.
Cover the potatoes with a layer of refried beans. Top that with the rest of the potatoes. Spread about 1/2 the salsa over the layers followed by 1/2 of the cheese.
Crack the eggs into a bowl, add the milk, and mix them with a whisk or fork. Add salt & pepper then pour eggs into the baking dish.
Top the layers with the remaining cheese. Cover dish with foil and bake about 45 minutes. At about 30 minutes you can remove the foil to allow the top to brown. When a knife comes out clean it’s ready.
Put the remaining salsa (warmed) on top as garnish.
Serve with warmed flour tortillas.
Serves 6 – 8.