Remove neck and giblets from turkey's body and neck cavities. Reserve for another use. Drain turkey of any juices; pat dry. Turn wings back to hold neck skin against back of turkey.
In bowl, mash together butter, Patak's Mild Curry Paste, minced garlic, chilli, cilantro, and lime juice.
Carefully work fingers under skin on breast of turkey. Place butter mixture under breast area.
Stuff cavity with lemon wedges. Return legs to tucked position.
Place turkey, breast side up, on flat rack in shallow roasting pan. Rub lightly with oil. Sprinkle with salt and pepper. Insert oven-safe meat thermometer in deepest part of thigh.
Roast in preheated 450 degrees F (230 degrees C) oven for 30 minutes. Reduce heat to 325 degrees F (160 degrees C). Add whole garlic cloves, sweet potatoes, carrots, onions, and rosemary. Cook until internal temperature reaches 180 degrees F (82 degrees C), legs move easily when twisted and juices run clear, about 2 to 2 1/2 hours.
Remove turkey from oven; transfer to platter. Discard lemons. Let turkey stand, covered with foil, 15 minutes.
To make gravy, strain vegetables, discarding rosemary. Reserve sweet potatoes, carrots and onions in bowl; Cover to keep warm. Pour pan juices into measuring cup, leaving brown bits in pan. Let fat rise to the top; remove 2 tbsp and place in roasting pan. Skim remaining fat and discard. Reserve remaining pan juices. (Should be about 2 1/2 cups.)
Place pan on stove over low heat. Whisk in flour; cook until lightly browned and bubbly. Stir in reserved juices. Cook, whisking and scraping up browned bits in pan, until smooth and slightly thickened. Taste; adjust salt and pepper if desired. Transfer to gravy boat.
Carve turkey as desired. Serve gravy and vegetables alongside.