Bring a large pot of water to a boil. Add the broccoli and blanch for 1 minute. Drain.
Place the butter in an ovenproof skillet (I prefer cast iron - especially a pan you've used for eons, so it's well-seasoned). Place the skillet in the oven for about 2 minutes, until the butter melts. Remove the pan from the oven and add the garlic and broccoli to the butter. Toss to coat. Arrange the lemon slices in the pan and season everything with salt and black pepper.
Roast for 5 to 8 more minutes, until the broccoli just starts to turn golden brown and the lemons are charred.