Best-Ever Yellow Squash Casserole

Ingredients (12)

• 1 tbsp vegetable oil
• 2 & 1/2 lbs yellow squashed
• 1 cup onion
• 8 oz. sour cream
• 1/4 cup mayonnaise
• 1 tsp Kosher salt
• 1/2 tsp freshly ground black pepper
• 1 1&2 cups cheddar cheese
• 1/2 cup Parmesan cheese
• 1 large egg
• 1 sleeve Ritz crackers
• 2 tbsp unsalted butter