Potatoes Au Gratin

Potatoes Au Gratin

spendwithpennies.com

  • 1 hr 50 min
  • Serves 8
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2½ lb red potatoes
1 medium onion, thinly sliced
3 tbsp butter
1 tsp dry mustard powder
2 cups milk
1 cup shredded cheddar cheese
½ cup shredded gruyere cheese
¾ tsp salt, divided
½ tsp black pepper, divided