Asparagus Casserole with French Fried Onions

Homemade French Fried Onions (or use store-bought):

• 3 large onions sliced into thin rings
• 1 1/2 cups milk
• 1 1/2 cups all-purpose flour
• 1 teaspoon garlic powder
• 1/4 teaspoon salt
• 1/4 teaspoon ground black pepper
• vegetable or canola oil for frying

Asparagus Casserole:

• 4 tablespoons unsalted butter
• 2 pounds fresh asparagus trimmed and cut into 1-inch pieces
• 8 ounce package white mushrooms sliced
• 1 small onion thinly sliced
• 1/4 cup all-purpose flour
• 1 1/2 cups light cream
• 1/2 cup mayo
• 1/2 cup cream cheese softened to room temperature
• 1/2 cup cheddar cheese shredded
• 1/2 cup Swiss cheese shredded
• 1/2 teaspoon thyme
• 1 teaspoon lemon zest
• 1/4 teaspoon paprika
• 1/2 teaspoon salt
• 1/4 teaspoon pepper