In a large skillet over medium heat, melt the butter. Stir in the tomato paste and cook for a few minutes, stirring occasionally.
Add the mushrooms and tomatoes and cook for 5 minutes, stirring occasionally, until the mushrooms are soft and the tomatoes are beginning to burst.
Add the garlic and cook for another 3 minutes, stirring occasionally, until the garlic is fragrant.
To make the sauce, pour heavy cream and Parmesan into the skillet and season with salt, pepper, and a pinch of red pepper flakes.
Simmer until slightly thickened, then add spinach and cook for 5 minutes, stirring occasionally, until the spinach is wilted and the sauce is creamy.
Garnish with basil before serving.
