Clean the Brussels sprouts and trim off the bottom 1/4 inch of their core, and remove any loose outer leaves. Cut a small slit in the bottom of each sprout with a small sharp knife.
Fill a large bowl with cold water (add some ice if not cold enough) and set it aside. Bring an inch or so, of lightly salted water to boil in a large pot. Add the sprouts and cover. Cook for 3-5 minutes, or until the sprouts are just barely tender. Cut one in half to check. Drain the sprouts and plunge immediately into the bowl of cold water. Leave them there for a few moments then drain again.
Cut the sprouts in half and place in a large bowl. Season sprouts to taste with salt and pepper, then toss with the lemon zest, shallots, parsley, and minced garlic.
Make the dressing: Whisk (or shake in a jar) the olive oil and lemon juice together vigorously until thick and pale yellow.
Pour the dressing over the sprouts and toss.
Refrigerate for at least an hour -- but note that these are really a lot better, a day after cooking.