Cook pasta until al dente.
Add basil leaves, 1/2 cup Parmesan, pine nuts, and salt and pepper to a food processor or blender. Turn machine on, then drizzle in olive oil while it mixes. Continue blending until combined, adding additional olive oil if needed. Set aside.
Heat cream and butter in a small saucepan over medium-low heat. Add pesto and stir.
Drain pasta and place in a serving bowl. Pour pesto cream over the top. Toss to combine. Add diced tomatoes and toss quickly. Serve immediately.