Cook the tortellini according to the package instructions. While the tortellini is boiling, start preparing the sauce. In a large skillet over medium heat, melt the butter. Add the minced garlic and cook, stirring, until fragrant, about 1 minute. Sprinkle the flour over the butter and garlic, stirring until it absorbs the butter, forms a paste, and begins to emit a nutty aroma. Gradually whisk in the heavy cream; initially, the mixture may appear thick and lumpy, but it will smooth out and thin as you continue whisking. Add the salt and grated Parmesan cheese, then let the sauce simmer for about 5 minutes until it thickens. Stir in the thinly sliced spinach and sun-dried tomatoes. Finally, add the drained tortellini to the skillet and gently toss to coat the pasta evenly with the sauce. Serve immediately.