Step 1
Line a rimmed baking sheet with foil and set a wire rack inside. Pat one 12–14-lb. turkey, neck and giblets removed, dry with paper towels and place, breast side up, on rack. Mix 1 Tbsp. ground cumin and ⅓ cup Diamond Crystal or 3 Tbsp. plus 1¼ tsp. Morton kosher salt in a small bowl to combine. Pat dry brine all over sides and in cavity of turkey, working into crevices. Chill turkey, uncovered, at least 1 day.
Step 2
Let turkey sit at room temperature 1–2 hours (no need to rinse off salt).
Step 3
Place a rack in middle of oven; preheat to 400°. Arrange turkey, breast side
up, on a wire rack set inside a rimmed baking sheet (if using the same baking sheet,
discard foil and rinse pan to remove any accumulated salty liquid). Pour 1 cup water
into baking sheet (this will keep the drippings from burning). Roast turkey, rotating
baking sheet halfway through, until golden brown, 35–45 minutes.
Step 4
Meanwhile, cook 3 garlic cloves, smashed, one 3″-long strip lemon zest, and 1 cup ghee in a small saucepan over medium, stirring occasionally and reducing heat to maintain a gentle sizzle if needed, until ghee is infused with flavor, 8–10 minutes.
Step 5
Remove turkey from oven and brush or spoon some infused ghee over turkey.
Reduce oven temperature to 300°. Return turkey to oven (if any spots are overly dark,
like the wing tips, cover with small pieces of foil) and continue roasting, rotating
baking sheet and brushing turkey with infused ghee every 15 minutes, until well browned
and an instant-read thermometer inserted into the thickest part of the breast registers
155° (temperature will continue to rise as the turkey rests), 70–80 minutes more. Let
turkey rest on baking sheet at least 30 minutes and up to 1 hour before serving.
Step 6
Remove and discard garlic and lemon zest from remaining ghee (you should have
about ½ cup; add more ghee to reach ½ cup if needed).
Step 7
Place 1 Tbsp. cumin seeds and 1½ tsp. fennel seeds in a small resealable plastic bag; seal and coarsely crush with a rolling pin. (You can also use a mortar and pestle.)
Step 8
Add crushed spices, 30 fresh curry leaves (if using), 1½ tsp. black mustard seeds, 1 tsp. Kashmiri chile powder, and remaining 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt to ghee. Heat over medium-high, stirring often, until mustard seeds begin to pop and curry leaves are crisp, about 2 minutes. Set tadka aside in a warm place (like the back of the stove) until ready to serve.
Step 9
Lift and tilt turkey so that all of the drippings from the bird run onto baking sheet; transfer turkey to a cutting board. Pour drippings into a large heatproof measuring glass, scraping in any browned bits stuck to baking sheet with a spatula. Pour in 2½–3 cups turkey stock or low-sodium chicken broth to make 3 cups mixture total.
Step 10
Melt 3 Tbsp. unsalted butter in a medium saucepan over medium heat. Add ¼ cup (31 g) all-purpose flour and cook, whisking constantly, until smooth and golden, about 3 minutes. Gradually pour in drippings mixture, whisking constantly until combined. Reduce heat to low and simmer, whisking often, until gravy is thick enough to coat a spoon, 12–18 minutes. Remove from heat; whisk in 2 Tbsp. Worcestershire sauce, 1 Tbsp. soy sauce, and 1½ tsp. sherry vinegar or red wine vinegar. Taste gravy and season with salt if needed and lots of freshly ground pepper. Transfer to a gravy boat or small bowl.
Step 11
Carve turkey as desired and arrange on a platter. Spoon tadka over and serve with gravy alongside.
Do Ahead: Turkey can be dry-brined 2 days ahead. Keep chilled, uncovered.