Melt butter in a non-stick pan over medium-high heat.
Sauté chopped onion until softened (~3-5 minutes).
Add garlic and cook for 1-2 minutes until fragrant.
Add spices, then flour, and toast for a minute.
Add milk and cream, cook on low heat until the sauce thickens.
Turn off the heat, add spinach and Parmesan cheese, taste, and adjust as needed.