Melt butter. Add onion and garlic and sauté for 1 minute.
Add chicken and cook until it changes from pink to white but not fully cooked.
Reduce heat and the milk, stirring as you go.
Add broth, rice, thyme and a just pinch of salt and pepper.
Stir, bring to simmer, and cover. Turn down to medium low and cook for 12 minutes.
Ad spinach in batches mixing it in as you go. Cook for 3 minutes until spinach is wilted.
Fold in the cheese and stir until melted.