If using broccoli raab, remove large leaves and, if necessary, cut stems into 6- to 8-inch lengths. In a 6- to 8-quart Dutch oven, cook broccoli, half at a time if necessary, in a large amount of boiling water until crisp-tender, allowing 3 minutes for broccoli raab or 6 minutes for broccoli florets. Drain well; gently squeeze broccoli if necessary to get it really dry.
In the same Dutch oven, heat oil over medium heat. Add garlic; cook and stir for 30 seconds. Carefully add drained broccoli raab or broccoli florets (the oil will spatter if the broccoli is not well drained); cook and stir for 1 minute.
Add broth. Cook, uncovered, until all of the broth is evaporated, stirring frequently. Stir in pepper and salt.