The first step is to roast the vegetables. Preheat the oven to 375, then clean and chop the sprouts and celery root* and coat with a little olive oil and salt and pepper. You can put them on the same baking sheet if you want, as long as you keep them separate so you can take them out at different times. The sprouts should take 10-15 minutes; take them out when a few are starting to brown and they're all easy to stab with a fork. The celery root pieces should be about the size of the brussels sprouts pieces, but will take about twice as long. Once they're soft to the touch, take them out as well but don't turn off the oven - you'll need it for the duck.
[*Celery root (AKA celeriac) is something most people I know don't really eat, but it's easy to do and quite tasty. It has a faint flavor of celery and carrot and a texture somewhere between a parsnip and a potato. It looks like a horrible dirt clod when you buy it, but you just slice off the outside layer and rinse off your knife and then you're good to go.]
When you're a few minutes away from taking the celery root out of the oven, get the duck going in a big skillet you can put in the oven later. Put it on very high heat, get it ripping hot, and add a little oil. Salt and pepper the skin side of the duck breast and put it down in the oil. Sear it for a few seconds and immediately turn the heat down to medium (on an electric stove go ahead and turn off the eye before you even put the breast in). You want to render out the fat layer without burning the skin. Once you've extracted a couple tablespoons of fat and the edges of the breast are starting to develop a well-done greyish look, salt and pepper the meaty side of the breast and turn it over in the pan. Let that cook for a minute, then into the oven for five more minutes or so (make it ten if you're an idiot and you take your duck well-done).
While that's going, work on the celery root. Melt a pat of butter over medium heat, then fry a clove or so of garlic for a minute. Add a couple big leaves of chiffonaded sage and a pinch of salt, let that all mix together for a minute, then take it off the heat. Drop in the pieces of roasted celery root, add a splash of milk or cream, and mash together. Set aside but keep warm.
When the duck is done, pull it out of the oven and set the breast aside to rest. Leave the fat in the pan - if you thought bacon grease was good, wait til you fry something in duck fat (Bobby, we'll talk). Add a thinly sliced shallot and a little salt to the pan and cook until the shallot's soft. No need to put the pan back on the fire - there should be enough residual heat from the oven to finish up. To the cooked shallot, add the sprouts and a couple of dried cranberries, then toss to mix and coat.
Slice the breast on a bias after it's rested for a few minutes. Put down the mash, and top with the sprouts and the duck. Garnish with a tiny leaf of sage (mine didn't make the photo). Serve with a wine you'd serve with Thanksgiving dinner.
