Fettucini Alfredo

I got this recipe from my friend Rebecca who lived by me in Logan. It is one of the best Alfredo recipes I have ever had!
3 Tbs. butter
3 Tbs. flour
1 c. heavy whipping cream
1 c. milk
3/4 c. fresh parmesan cheese
1/2 c mozzarella cheese l/2 tsp. garlic salt or 1 clove garlic, minced and 1/4 tsp. salt or to taste.
Pepper

Melt butter and add flour to make a paste. Gradually stir in milk and cream. Stir in garlic salt, and salt and pepper to taste. Stir constantly until thickened. Remove from heat and stir in cheeses. Return to heat until melted and smooth.