Meanwhile melt butter in pan over medium high heat. Add onion and garlic and cook several minutes till fragrant. Add spinach in batches and cook an additional 2-4 minutes until spinach is slightly wilted. Add salt, pepper, and hot sauce. Remove from heat and put in medium mixing bowl using slotted spoon so as not to add liquid from cooking.
Add dotted cream cheese to warm spinach and combine till melted.
Add remaining ingredients and combine well. Pour into casserole dish and top with additional parmesan cheese. Bake in preheated oven 20-25 minutes. Remove from oven let stand about 10 minutes. Serve warm.
Can be served with tortilla chips, crackers, or crusty bread