Frittata mudah

Bahan-bahan (6 porsi)

• 6 large eggs ($1.49)
• 1/4 cup milk ($0.06)
• 1/2 tsp salt ($0.03)
• 1/4 tsp pepper ($0.02)
• 2 Tbsp cooking oil ($0.08)
• 1 yellow onion ($0.36)
• 2 cups fresh spinach (about 4 oz.) ($0.99)
• 1 pint grape tomatoes ($2.00)
• 1/4 cup crumbled feta ($0.41)