Step 1

Cook garlic and 3 Tbsp. oil in a large ovenproof skillet over medium, reducing heat as needed to keep garlic from burning, until golden brown, 6–8 minutes. Add anchovies, tomato paste, and ½ tsp. red pepper flakes.

Step 2

Cook, stirring with a wooden spoon, until tomato paste is darkened in color and anchovies are dissolved into mixture, about 2 minutes.

Step 3

Add broccoli rabe to skillet and stir to coat; season with salt and pepper. Cook until broccoli rabe leaves are wilted and stems begin to soften, 6–8 minutes. Mash garlic cloves with spoon and stir into broccoli rabe to incorporate. Add tomato pieces and cook until broccoli rabe is tender and almost all of the liquid from tomatoes is evaporated (it should look more like a paste than a sauce), 8–10 minutes. Add beans, reserved tomato liquid, and ¼ cup water and stir to combine; season with more salt and pepper. Bring to a simmer and cook until beans are warmed through and flavors have melded, about 5 minutes.

Step 4

Heat broiler. Evenly scatter mozzarella over bean mixture and transfer skillet to oven. Broil until cheese is melted, bubbling, and browned in spots, about 2 minutes (watch carefully so cheese doesn’t burn).

Step 5

Serve beans, topped with Parmesan and more oil and red pepper flakes, with toast alongside for dipping.