Potato Frittata | Umami

Ingredients

• 1 med onion (cut into thin slivers)
• 2 tbsp butter
• 1 16 oz package hash brown potatoes
• 1 tsp salt (divided)
• 1/4 tsp black pepper
• 10 large eggs
• 1/2 cup milk
• 4 oz mascarpone cheese
• 4 oz sharp cheddar (grated)