Heat the oven to 275°.

Separate the garlic cloves from the bulbs and peel them, lightly crushing each clove with the flat side of a knife to loosen the skins.

If the duck fat is solid, warm it briefly in the microwave or in a small saucepan on the stove until just pourable.

Arrange the peeled garlic cloves in a small baking dish and pour the duck fat over until the garlic is completely submerged. Tuck in the thyme sprigs.

Transfer to the oven and bake until the garlic is soft, golden and fragrant, about 30 to 45 minutes, keeping the fat at a gentle simmer. If it bubbles too vigorously, lower the oven temperature slightly.

Let cool, then pour the garlic and duck fat into a heatproof container, making sure the cloves are fully covered. Refrigerate and use the duck fat and the garlic within one week, or remove the garlic from the fat and freeze the cloves and fat separately for up to six months.