Brussels Sprouts with Mustard-Caper Butter

Serves 8 or more. A zesty way to do up Brussels sprouts, romanesco, broccoli and/or cauliflower. This has become a staple at our Thanksgiving table.
Mustard-Caper Butter:
2 garlic cloves
sea salt and fresh pepper
6 Tbs. unsalted butter, at room temp
2 tsp. Dijon-style mustard
1/4 cup drained small capers, rinsed
grated zest of 1 lemon
3 Tbs. chopped marjoram, or 2 tsp. dried
Pound the garlic with 1/2 tsp salt in a mortar until smooth, then stir it into the butter with the mustard, capers, lemon zest, and marjoram. Season with pepper. Can be made a day ahead and then refrigerated. Bring back to room temp before serving.
The Vegetables:
1 lb. Brussels sprouts, or 1 whole stalk stripped of its sprouts
1 head romanesco and/or broccoli and/or cauliflower
Trim the base off the sprouts, then slice them in half or, if large, into quarters. Cut the cauliflower and broccoli into bite-size pieces.
Bring a pot of water to a boil and add salt. Add the Brussels sprouts and cook for about 3 minutes. Then add teh other veggies and continue to cook until tender, about 5 minutes.
Drain, shake off any excess water, then toss with the Mustard-caper butter. Taste for salt, season with pepper and toss again.