To a large pot of boiling salted water add the Brussels sprouts and cook for 10 minutes, remove with a slotted spoon and drop into a bowl filled with ice and water, after 5 minutes strain and set aside.
In a large saute pan over a medium flame heat some olive oil (very little). When it begins to smoke, add some chopped chorizo, and cook until it becomes crispy and has rendered some fat. Add some onion and garlic (optional) and cook until the onion is translucent, increase the flame to high. Add the sprouts and cook for an additional 3 minutes.
Add a cup of chicken/turkey stock and cook for 5 minutes, or until the liquid has reduced to approximately 1/4 cup, add a large knob of butter and cook for 3 more minutes, season with salt and pepper and serve in a large bowl.