Preheat oven to 350 degrees. Drain spinach well, pressing between paper towels.
Melt 2 tablespoons butter in a large Dutch oven over medium heat. Add onion, and sauté 5 minutes or until tender. Add garlic, and sauté 1 minute; remove from heat.
Stir cream cheese into onion mixture until melted and well blended. Stir in spinach, milk, and next 3 ingredients.
Stir together egg, drained pimiento, and 1 1/2 cups cheese; stir egg mixture into spinach mixture. Spoon mixture into lightly greased (with cooking spray) ramekins, or a 2 quart baking dish; sprinkle with salt and pepper.
Toss together panko, 2 tablespoons melted butter, and remaining 1/2 cup cheddar cheese; sprinkle over spinach mixture.
Bake at 350 for 50 minutes or until bubbly and golden.