Bring a large pot of salted water to a boil. Add the pasta and cook until just al dente, about 9 minutes. Before draining, scoop out 1 cup of starchy pasta water and set aside.
While the pasta cooks, steam or blanch the broccoli until vibrant green and tender-crisp, about 4-5 minutes. Drain and set aside.
Drain the soaked cashews and rinse them. In a blender, combine the cashews, lemon juice, garlic, a pinch of salt, and ½ cup of the reserved pasta water. Blend until completely smooth and creamy, about 1-2 minutes. If needed, add more water a tablespoon at a time to reach a silky consistency.
Heat the olive oil in a sauté pan over medium heat. Add the minced garlic and sauté until fragrant, about 30 seconds, until golden and aromatic.
Add the cooked broccoli to the pan. Toss gently and cook for 1-2 minutes, just to rewarm and coat in the garlic oil. The broccoli should stay bright and slightly crisp.
Pour the blended cashew sauce into the pan with the broccoli. Warm gently over low heat, stirring constantly, until the sauce thickens slightly and coats the vegetables evenly—about 2 minutes. If it gets too thick, stir in a bit more reserved pasta water.
Add the drained pasta into the pan. Toss everything together over low heat until the pasta is well coated and heated through, about 1 minute.
Remove from heat and let rest for a minute. Taste and adjust seasoning with salt, more lemon juice, or a pinch of red pepper flakes. Serve immediately, garnished with extra lemon zest or herbs if desired.
