Heat the oven: Preheat to 425°F (220°C).
Line a sheet pan with parchment for easy cleanup.
Prep the tomatoes: Toss halved tomatoes with 2 tablespoons olive oil, sliced garlic, 1 teaspoon salt, black pepper, and red pepper flakes if using. Spread in a single layer on the pan.
Roast: Bake for 18–22 minutes, until the tomatoes slump, edges caramelize, and the garlic is golden. Don’t overcook the garlic—aim for lightly golden, not brown.
Cook the orzo: Meanwhile, bring a large pot of salted water to a boil.
Cook orzo until just al dente according to package directions. Reserve 1 cup pasta water, then drain.
Make the basil cream: In a blender, combine cream, Parmesan, basil, remaining 1 tablespoon olive oil, lemon zest, and a pinch of salt and pepper. Blend until smooth and pale green.
If too thick, loosen with a splash of pasta water.
Combine: Return drained orzo to the pot. Add butter (if using), the roasted tomatoes and their pan juices, and half the basil cream. Toss gently.
Add more basil cream until it’s silky and coats the orzo. Splash in pasta water as needed to thin.
Finish: Squeeze in 1–2 teaspoons lemon juice to brighten. Taste and adjust salt and pepper.
Stir in most of the pine nuts, reserving some for topping.
Serve: Spoon into bowls. Top with extra Parmesan, torn basil, remaining pine nuts, and a drizzle of olive oil.