To brine the turkey
Line extra-large pot or bowl with two 13-gallon (or larger) plastic bags, 1 inside the other. Combine 1 quart water, salt, bay leaves, peppercorns, and allspice in large saucepan. Stir over medium heat until salt dissolves. Remove from heat. Add 1 quart cold water and cool to lukewarm. Pour into plastic bags; mix in remaining 6 quarts water. Wrap turkey neck and refrigerate. Submerge turkey in brine to cover completely, gathering bags tightly to eliminate any air; tie bags closed. Refrigerate turkey in brine in pot at least 18 hours and up to 20 hours.

Line large roasting pan with 4 layers of paper towels. Remove turkey from brine and drain well; discard brine. Place turkey in prepared pan. Cover with plastic wrap and refrigerate overnight.

For herb butter and gravy
Mix parsley, thyme, sage, marjoram, rosemary, and nutmeg in small bowl. Transfer 1/4 cup herb mixture to small bowl; mix in 1/2 cup butter.

Combine broth and apple cider in heavy large saucepan. Boil until reduced to 3 cups, about 20 minutes. Pour broth reduction into bowl. Melt remaining 1/4 cup butter in same saucepan over medium-high heat. Add flour; stir 1 minute. Whisk in broth reduction, then cream, Calvados, and remaining herb mixture. Bring to boil; reduce heat to medium-low and simmer until gravy base is thickened and reduced to 2 3/4 cups, whisking often, about 20 minutes. Cool gravy base slightly. (Gravy base and herb butter can be made 2 days ahead. Cover and chill.)

To roast the turkey
Position rack in bottom third of oven and preheat to 350°F. Remove turkey from roasting pan; drain any accumulated juices from main cavity. Discard paper towels from roasting pan. Melt herb butter in small saucepan over medium heat. Brush bottom of roasting pan with some of herb butter. Return turkey to prepared pan. Tuck wing tips under; tie legs together loosely to hold shape. Place some apple quarters and onion quarters in main cavity. Brush remaining herb butter over turkey; sprinkle with pepper. Scatter remaining apples and onions around turkey in pan. Add reserved turkey neck to pan.

Roast turkey 1 hour. Baste with 1/2 cup apple cider. Roast turkey 30 minutes. Baste with remaining 1/2 cup cider. Roast turkey until thermometer inserted into thickest part of thigh registers 175°F, basting turkey every 30 minutes with pan juices and covering breast loosely with foil if browning too quickly, about 2 hours longer (3 1/2 hours total). Transfer turkey to platter; let stand at least 30 minutes before carving (internal temperature will rise 5 to 10 degrees).

Discard apples, onions, and turkey neck from pan. Pour pan juices into large glass measuring cup; spoon off fat from surface. Pour degreased juices into gravy base and bring to boil over medium-high heat, whisking occasionally. Boil until gravy thickens enough to coat spoon and is reduced to 3 1/2 cups, about 15 minutes. Season gravy to taste with pepper.

Serve turkey with gravy.

For gravy base
Melt butter in heavy large deep skillet over high heat. Add turkey necks and/or wings and sauté until deep brown, about 15 minutes. Add onions, carrots, and celery and sauté until vegetables are deep brown, about 15 minutes. Add 6 cups chicken broth and bring to boil. Reduce heat to medium-low and simmer uncovered 45 minutes, stirring occasionally.

Pour gravy base through strainer set over 4-cup measuring cup, pressing on solids to extract liquid. If necessary, add enough chicken broth to gravy base to measure 4 cups. (Gravy base can be prepared 2 days ahead. Cool slightly. Refrigerate uncovered until cold, then cover and keep chilled. Rewarm before using.)

For turkey
Mix 1/2 cup butter and all minced herbs in small bowl; season herb butter with salt and pepper. Transfer 2 generous tablespoons to another small bowl and reserve for gravy; let stand at room temperature.

Set rack at lowest position in oven and preheat to 425°F. Rinse turkey inside and out; pat dry. Starting at neck end, slide hand between skin and breast meat to loosen skin. Rub 4 tablespoons herb butter over breast meat under skin. Place turkey on rack set in large roasting pan. Sprinkle main cavity generously with salt and pepper. Place 4 tablespoons plain butter and all fresh herb sprigs in main cavity. Tuck wing tips under. Tie legs together loosely. Rub remaining herb butter over outside of turkey. Sprinkle turkey generously with salt and pepper.

Place turkey in oven and roast 20 minutes. Reduce oven temperature to 350°F. Roast turkey 30 minutes; pour 1 cup broth over and add 1 tablespoon plain butter to roasting pan. Roast turkey 30 minutes; baste with pan juices, then pour 1 cup broth over and add 1 tablespoon butter to pan. Cover turkey loosely with foil. Roast turkey until thermometer inserted into thickest part of thigh registers 175°F, basting with pan juices and adding 1 cup broth and 1 tablespoon butter to pan every 45 minutes, about 1 hour 45 minutes longer. Transfer turkey to platter; let stand 30 minutes (internal temperature will rise 5 to 10 degrees).

Strain pan juices into bowl; whisk in gravy base. Melt reserved 2 tablespoons herb butter in heavy large saucepan over medium heat; add flour and whisk constantly until roux is golden brown, about 6 minutes. Gradually add pan juice-gravy base mixture; increase heat and whisk constantly until gravy thickens, boils, and is smooth. Reduce heat to medium; boil gently until gravy is reduced to 4 1/2 cups, whisking often, about 10 minutes. Season gravy with salt and pepper.