Prepare the duck: Using the tip of a sharp knife, prick the meaty part of each duck leg. Next, rub each leg with the minced garlic, followed by salt and pepper.
Preheat oven: To 250 F degrees.
Roast: Place the duck legs down in a roasting pan lined with a rack. Next, add in the thyme, first portion of red pepper flakes, and a 1 /2 cup of water. Finally, cover the pan with aluminum foil and cook for about 2 hours - until all the fat is rendered.
Roast again: Remove the duck from the oven and remove the aluminum foil and rack. Turn the duck legs skin side up and place them back in the roasting pan in the fat. Finally, re-cover with aluminum foil and cook again for another 2 1/2 hours or until the meat is very tender.
Make the sauce: In a medium-sized saucepan over medium-high heat, add the vinegar, sugar, mustard seeds, red pepper flakes, rosemary, 1 sprig thyme, and 1 cup of water. Next, bring to a boil and then reduce heat and simmer - stirring until sugar is dissolved. Finally, mix in the raisins, remove from heat, and let cool for 1 hour.
Finish: Increase the oven temperature to 400 F degrees and remove the duck legs. Place the duck legs skin side up on a baking sheet or roasting pan lined with a rack or even just parchment paper and then place back into the oven and roast for another 30 - 35 minutes or until skin is brown and crisp.
Serve: Transfer the duck legs to a serving platter and pour the pickled raisin sauce over the duck legs, garnish with thyme, and serve!