Bring stock to a boil in a saucepan, then reduce heat to a low simmer.

Melt butter in a large, heavy bottomed stock pot over medium heat. Add onion; cook until softened, 2 minutes.

Add rice; cook until lightly toasted, 2 minutes, stirring constantly. Gradually add simmering stock, stirring continuously. Risotto will become “creamy” and slightly sticky. When almost finished, stir in zucchini, sun-dried tomatoes, and thyme, adding stock as needed and stirring continuously. When finished, the rice should be tender yet firm to the bite.

Stir in 3 tablespoons Parmesan cheese and basil just before serving; divide among six bowls. Sprinkle servings with remaining 3 tablespoons cheese; season with black pepper.