Place an empty sheet pan into the oven and preheat to 400°F. Place
the romanesco florets into a large bowl, drizzle with olive oil, salt, and pepper, and toss to combine.
Remove the preheated sheet pan from the oven and carefully turn the florets out in an even layer onto the hot pan. Return the pan to the oven and roast romanesco until tender and golden brown, approximately 25–30 minutes.
Dip
Meanwhile, in a food processor, pulse the beans, olive oil, lemon juice and zest, garlic, salt, and pepper until combined. If you desire a smoother consistency, keep the food processor running while slowly adding up to
4 tablespoons water. Process until smooth. Blend in the fresh rosemary.
Serve
Serve family style: spoon the white bean dip onto a platter, drizzle with some olive oil, sprinkle with vegetable ash (optional), and place florets all around.