If using the topping, heat 1 tablespoon olive oil in a small skillet over medium heat. Add the panko and stir frequently until deep golden, about 4 minutes. Set aside.

Bring a pot of well-salted water to a boil. Cook the broccoli florets and sliced stem for 3 minutes, then remove them with a slotted spoon. Cook the pasta in the same water according to its package directions.

Combine 4 tablespoons olive oil and the garlic in a wide cold pan. Warm over low heat until the garlic sizzles gently. Add the red pepper flakes and cook for 30 seconds without browning the garlic.

Add the cooked broccoli. Press and mash some of the florets with a wooden spoon over low heat, leaving some texture.

Reserve 1/2 cup pasta cooking water and add it to the broccoli pan. Bring to a simmer, then stir in the lemon juice and black pepper.

Add the pasta and toss, adding more pasta water if needed. Season with salt. Reduce the heat to low, sprinkle the Parmesan over the pasta, and leave it undisturbed for 1 to 2 minutes before tossing until creamy.

Divide among bowls and finish with extra Parmesan and the toasted panko, if using.