Cut the garlic bulb in half and put it in a small mixing bowl. In a separate bowl, put the cleaned gizzard and rub in some salt, then rub it with the garlic followed by the thyme. Let the gizzards sit in the refrigerator for approximately 3 hours.
After this time take them out of the fridge and the marinade and rinse under cold water.
In a heavy-bottomed pan over a medium-high heat with a slick of duck fat, roast the gizzards for a couple of minutes. Meanwhile, in another saucepan gently heat the remaining duck fat over a medium heat. Slide the gizzards into the duck fat and move the pan to the oven to cook for 2 hours.
Lift the gizzards from the fat with a slotted spoon and drain any excess fat on paper towels. Slice the gizzards and use them for canapés, garnish on rice or even as a spread on toast.