Asparagus and Swiss Cheese Frittata

Bahan-bahan (4 porsi)

• 1/2 lb asparagus (tough ends trimmed off)
• 1/2 cup shallots (chopped)
• 2 teaspoons salted butter
• 5 large eggs
• 4 large egg whites* ((1/2 cup))
• 2 tbsp fresh grated Pecorino Romano
• 3 oz part-skim Swiss cheese
• 1/2 tsp kosher salt and fresh pepper to taste