Ingredients

1. Two 7-to-8 pound capons, necks and gizzards reserved for the sauce
2. 1 pound shiitake mushrooms, stems reserved, caps thickly sliced
3. 1/2 ounce dried porcini mushrooms (1/2 cup)
4. 6 cups chicken stock
5. Salt and freshly ground pepper
6. 1 1/2 sticks plus 2 tablespoons
7. (7 ounces) unsalted butter, softened
8. 1/4 cup snipped chives
9. 1/4 cup finely chopped flat-leaf parsley
10. 1 1/2 teaspoons minced garlic
11. 1 teaspoon fresh lemon juice
12. 3 tablespoons extra-virgin olive oil
13. 2 large shallots, minced (1/2 cup)
14. 2 tablespoons all-purpose flour
15. 1/2 cup dry Madeira
16. 1/2 cup water

Directions

1. In a medium saucepan, combine the reserved capon necks and gizzards with the shiitake stems, dried porcini and chicken stock and bring to a boil.  Reduce the heat to moderate and simmer until reduced to 2 cups, about 1 hour and 15 minutes. Strain the stock into a heatproof bowl, pressing hard on the solids. Season lightly with salt and pepper.
2. Meanwhile, preheat the oven to 350°. In a food processor, puree 1 1/2 sticks of the butter with the chives, parsley, garlic, lemon juice and 1/2 teaspoon of salt. Using your fingers and starting at the neck, gently loosen the capon skin from the breast and legs. Rub all but 2 tablespoons of the herb butter under the skin of the birds; press gently on the skin to evenly distribute the butter.
3. Set the capons on 2 racks in 1 large or 2 medium roasting pans. Rub with 1 tablespoon of the olive oil and season generously with salt and pepper. Roast the capons for about 1 hour and 40 minutes, or until golden and an instant-read thermometer inserted in the inner thigh of each capon registers 170°. The juices in the cavity will still be slightly pink. Transfer the birds to a carving board, cover loosely with foil and let stand for at least 10 minutes or for up to 30 minutes. 
4. Meanwhile, in a large, deep nonstick skillet, heat the remaining 2 tablespoons of olive oil. Add the shiitakes, season with salt and pepper and cook over moderately high heat until browned, 8 minutes. Add the remaining 2 tablespoons of unsalted butter and cook, stirring, until melted. Add the shallots and cook, stirring occasionally, until golden, about 6 minutes.
5. Add the flour to the mushrooms and cook, stirring, for 2 minutes. Add the Madeira and bring to a boil, stirring constantly, for 1 minute longer. Add the strained stock and bring to a boil, stirring. Reduce the heat to moderately low and simmer for 30 minutes. Whisk in the remaining 2 tablespoons of herb butter and season with salt and pepper; keep warm.
6. Pour the juices from the roasting pan into a heatproof bowl and skim off the fat. Set the roasting pan over 2 burners on high heat, add the water and scrape to release any browned bits from the bottom; add to the pan juices in the bowl. Strain the pan juices into the Madeira sauce, along with any accumulated drippings from the capons; stir and season with salt and pepper. Carve the birds and serve them with the Madeira sauce on the side.

Make Ahead

Make the stock and butter the capons up to 1 day ahead. Bring the capons to room temperature before roasting; finish the sauce while the birds rest before carving.