6 oz Brussels sprouts
1 bunch red radishes, about 1-1/2 inches in diameter
4 tbsp unsalted butter
1 tbsp shallot, minced
1/4 tsp granulated sugar
1/4 tsp champagne vinegar, plus more to taste
Kosher salt and freshly ground black pepper
1/4 cup chicken stock or vegetable stock, plus more if needed
3 kohlrabi, about 2-1/2 inches in diameter
1 tbsp chives or mint, finely chopped (we used chives)
Bring a large pot of salted water to a boil. Prepare an ice bath. Meanwhile, trim the root ends of the Brussels sprouts and remove and discard any tough or bruised outer leaves. Cut the sprouts in half through the root end.
Blanch the sprouts until tender, about 4 minutes. Chill in the ice bath and drain.
Trim the greens from the radishes and wash the radishes under cold water. Cut larger radishes into 6 wedges each, smaller radishes into quarters.
Melt 2 tbsp of the butter over medium heat in a sauté pan big enough to hold the radishes in a single layer. Add the shallot and cook for 2 to 3 minutes, stirring often, until softened. Add the radishes. sugar, and vinegar, season generously with salt and pepper, and add 2 tbsp of the stock. Bring to a simmer, cover the pan, and simmer gently for about 8 minutes, until the radishes are crisp-tender. Cook uncovered, swirling the pan, to glaze the radishes, about 2 minutes (the recipe said to cook for 4 minutes to glaze, but I was impatient). Pour radishes into a small bowl and set aside.
Return the large pot of salted water to a boil and add more water if necessary.
While the radishes are braising, cut the stems and roots from the kohlrabi. Stand each kohlrabi on a cut end and peel it with a sharp knife, cutting deep enough to reach the tender flesh. Cut lengthwise into slices about 1/2 inch thick. Trim the rounded sides of the slices and cut the kohlrabi into 1/2-inch-wide batons. You need 2 cups of batons (reserve any remaining kohlrabi for another use).
Add the kohlrabi to the boiling water and cook for 5 minutes, or until tender. Drain and transfer to paper towels to drain thoroughly.
Add the remaining 2 tbsp stock to the large sauté pan. Bring to a simmer. Whisk in the remaining 2 tablespoons butter until emulsified and smooth. Add the Brussels sprouts and kohlrabi and cook over high heat for 45 seconds. Add the radishes and any liquid remaining in the bowl and heat through. If the butter begins to break, you can swirl in another couple of tablespoons of stock or water. Toss in the chives and season with salt and pepper and a few drops of vinegar, or to taste. Transfer the vegetables to a platter.
Serve vegetables topped with sliced duck breast.