Bring a large pot of salted water to a boil. Add pasta and cook according to package directions. Once cooked, drain cooked pasta in a colander and set aside.
While pasta is cooking, add milk and spinach to a blender and blend until milk is green and spinach is totally pureed.
Place the empty pot back on the stove. Add the butter to the pot and melt over medium heat. Once melted, add in the flour and cook for 30 seconds, while stirring.
Grab a whisk and slowly pour the milk/spinach mixture into the pot while whisking to prevent lumps.
Bring the pot up to a simmer to thicken, then stir in the grated cheese, garlic powder, and salt.
Turn off the heat. Add the cooked pasta to the pot and stir until pasta is fully coated with the sauce. Taste and add more salt or cheese as needed.
Enjoy warm or let leftovers cool and store in an air-tight container in your fridge for up to 4 days.
