Preheat oven to 375 degrees. Spray a medium casserole dish with non-stick cooking spray.
Pour 1 cup of the sauce into baking dish and tilt dish to spread. Drizzle in 3 Tbsp heavy cream and stir (it doesn't need to be fully incorporated). Add half the tomatoes.
Bring a large pot of unsalted water to a boil. Cook gnocchi about 1/3 shy of the time listed on package (they continue to cook in the oven).
Drain gnocchi well then immediately transfer to baking dish and spread out. Sprinkle in remaining tomatoes, then pour remaining 1 cups sauce evenly over top*.
Top with mozzarella cheese.
Bake in preheated oven until sauce is bubbling, about 10 - 12 minutes. If you'd prefer cheese browned a bit then broil closer to broiler element during the last 2 - 4 minutes of that cook time.
Garnish with basil and serve warm.