Cook pasta according to directions listed on package to al dente. Drain pasta. In a medium saucepan, melt butter over medium heat.
Once butter has melted, add in flour and cook, whisking constantly, 1 minute. Slowly pour in milk and cream while whisking.
Increase heat to medium-high and bring mixture just to a boil, stirring constantly, then reduce heat to low. Stir in fresh mozzarella, and cook, stirring constantly until melted.
Season with salt and pepper to taste. Toss in drained pasta and let rest over warm heat for 2 - 3 minutes. Plate pasta and top with diced tomatoes and fresh basil.