Penne in spinach cream sauce

My kids love pasta, and whenever the father is not at home, I end up making pasta for dinner. The addition of spinach is my sole concession to make it "healthy".

200 gms penne pasta
1 tbsp butter
2 tbsp cornflour
2 cup milk
2 garlic cloves, minced
4 tbsp cheese, grated
1 bunch spinach, washed and cut
Salt and pepper to taste
2 tbsp chopped walnuts, and a few more for garnishing

Method:
Cook the pasta according to the instructions on the packet. Pour cold water to stop further cooking, drain and keep aside.
Heat the butter in a pan, add the garlic and when the aroma fills the room, add the spinach and saute till most of the water is released and evaporated. Remove from pan and keep aside.
In the same pan, bring the milk to boiling.
When the milk is slightly warm, use some of it to make a paste with the cornflour.
After the milk comes to a boil, add the cornflour paste, stirring constantly to ensure no lumps are formed. Add salt and pepper, and cheese. Turn off the flame.
Mix the spinach and the broken walnuts with the pasta, and add the white sauce. Garnish with walnuts and serve