In a skillet, add butter over medium heat.
Once melted, add garlic and sautee for one minute.
Add flour, whisking to combine with butter and garlic mixture.
Let cook for 1 minute, stirring so it doesn't burn.
Slowly add the milk in 1/2 cup increments, whisking to fully stir it in with the butter/flour mixture. Adding it slowly and whisking it together will ensure it does not clump.
Once all the milk is added, bring to a simmer.
Lower heat to low and let simmer for about 5-7 minutes, until it begins to thicken.
Add gnocchi, and let simmer for another 7-10 minutes, stirring occasionally. During this time, the gnocchi will cook and the sauce will thicken more.
Once sauce is to your preferred consistency, add about 3/4 of the mozzarella and season with salt and pepper. Stir to mix the mozzarella and salt/pepper in with the sauce.
Top with fresh basil, tomatoes, and remaining mozzarella.
Serve and enjoy!