In a large mixing bowl mix: cauliflower and broccoli heads with salt, pepper, lots of garlic, and olive oil. Place the mixture on a large cookie sheet and roast the vegetables for about 25 minutes at 450 degrees. While that is cooking melt somewhere between 1/2 and 2/3rds of a stick of butter, the juice of 2 lemons, and 4 TBS of whole grain mustard ... and more garlic ... why not? When the vegetables are done put them back in the mixing bowl and pour the butter sauce over them. Transfer to a baking dish for serving. Do this 2 hours before you plan to eat as this needs to sit at room temperature for 2 hours. When you reheat to serve, do not use the microwave! Heat in the oven for about 10 minutes.
I also used some stuff I bought at Costco that is actually used for garlic bread. I used this before roasting; I mixed it in with the vegetables before roasting them. You don't have to use this stuff, but if you see it at Costco buy it; I use it for lots of things. I'll post a picture of it next week so you will know what to buy.