1. Cut the chicken breasts into medium chunks and season lightly with salt and black pepper.
2. In a large saucepan or wide pot over medium heat, melt all the butter.
3. Add the chicken and cook gently for 6–8 minutes, stirring occasionally, until fully cooked and lightly golden but not browned.
4. Remove the chicken from the pot using a slotted spoon and set aside. Leave all the butter and juices in the pot.
5. Reduce heat to medium-low. Sprinkle the flour into the butter and whisk continuously for about 1 minute to form a smooth roux without browning.
6. Slowly pour in the warm milk while whisking constantly to keep the sauce smooth.
7. Cook, whisking often, for 5–7 minutes, until the sauce thickens and coats the back of a spoon.
8. Remove from heat and stir in the grated Parmesan until fully melted and smooth.
9. Add the garlic powder, then return the cooked chicken to the sauce. Stir until evenly distributed.
10. Season with additional salt and black pepper to taste.
11. Let the sauce cool completely, then portion into 10 servings of 1 cup/ - 240ml before freezing.
