Boil the tortellini according the package directions.
While the tortellini is cooking, prepare the sauce. Melt the butter in a large skillet over medium heat. Add the garlic and cook, stirring, until fragrant, about 1 minute. Sprinkle in the flour and stir until it has absorbed the melted butter, becomes a paste and begins to smell nutty. Slowly whisk in the heavy cream (at first the mixture will be thick and chunky, but it will smooth and thin out), then add the salt and Parmesan cheese. Allow to simmer until thickened, about 5 minutes.
Stir in the spinach and sun-dried tomatoes, then transfer the cooked and drained tortellini to the skillet, gently stirring to coat the tortellini with the sauce. Serve immediately.