Step 1Heat the oven to 375 degrees. Prepare the potatoes: Place a potato in a tablespoon and cut it into one-fourth-inch slices joined at the base (the spoon will prevent the knife from slicing all the way through). Open the slices just slightly and place a piece of bay leaf and a sprig of thyme inside the potato. Repeat with the remaining potatoes and place them in a roasting pan just large enough to hold them.
Step 2Drizzle the fat over the potatoes and season them with three-fourths teaspoon of salt and one-fourth teaspoon of pepper, or to taste. Place the pan on the stove top on medium-high heat and cook just until the fat begins to bubble, 2 to 3 minutes.
Step 3Place the pan in the oven and roast the potatoes, basting them occasionally with the fat, until browned and crisp, 45 minutes to 1 hour. (The recipe can be prepared up to this point one day ahead; cool the potatoes slightly, then cover and refrigerate them overnight.)
Step 4To reheat the potatoes, warm in the roasting pan briefly on the stove top over medium-high heat, about 2 to 3 minutes, then transfer to a 375-degree oven for 15 to 20 minutes until thoroughly warmed.