Agave-Glazed Turkey Breast with Sherry Gravy

Pat turkey breast dry and rub all over with 2 1/2 teaspoons sea salt and 1 teaspoon pepper. If you have the time, chill the breast in a baking dish, covered, overnight (see Cooks' Notes).

Let turkey stand at room temperature 1 hour.

Heat oven to 425°F with rack in lower third. Position turkey on rack in pan and roast 30 minutes.

Reduce oven to 400°F and scatter onion slices in bottom of roasting pan. Add 1 cup water and continue to roast until thermometer inserted in thickest part of breast, close to but not touching bone, registers 160°F, 30 to 40 minutes.

While turkey is roasting, stir together agave nectar and vinegar in a small nonreactive saucepan and boil, stirring occasionally, until thickened and reduced to 3 tablespoons. Remove from heat, but keep warm.

Brush glaze on turkey and roast until thermometer registers 165°F, 3 to 5 minutes.

Transfer turkey breast to a platter and let stand 15 minutes.

While turkey is standing, remove the rack, scraping off any yummy bits into the pan.

Straddle pan over 2 burners and add sherry, then deglaze pan by boiling sherry, stirring and scraping up browned bits, for 1 minute.

Strain liquid through a sieve into a heavy medium saucepan. Add stock and bring to a boil. Reduce heat and keep at a simmer.

Meanwhile, whisk 1/2 cup water slowly into flour in a small bowl until flour slurry is smooth, then whisk in 1 tablespoon vinegar. Add flour slurry to simmering stock, whisking, and bring gravy to a boil, whisking. Reduce heat and simmer, whisking, 3 minutes.

Season gravy with salt and pepper and additional vinegar, if desired.

Slice turkey breast and serve with gravy.