Preheat the oven to 220 degrees Celsius/ 430 degrees Fahrenheit. Lightly butter a casserole dish of about 20x25 cm/ 8x10 inches.
Prepare potatoes: Peel the potatoes and slice them thinly, about 2-3 mm/ 0.07 – 0.11 inches thick. Using a mandolin/slicer makes things easier and faster. Spread the potato slices in the prepared casserole dish.
Mix the heavy cream, grated garlic, and herbs. Add ½ teaspoon fine sea salt and black pepper. Pour the mixture over the potatoes and shake the casserole dish slightly to ensure that the cream is evenly distributed in the dish.
Prepare chicken: Remove the fat and skin wobbling on the underside of the chicken thigh. Only leave the skin surrounding the drumstick and the skin on the upper side of the chicken thigh. Pat the chicken quarters dry with kitchen paper. Rub well with salt, pepper, and sweet paprika. Place the chicken legs on top of the potatoes.
Bake the potato gratin for 1 hour or until the chicken is cooked through and the potatoes are soft. To check if the chicken is cooked through, pierce it in the thickest part of the thigh, the juices should run clear.
Preferably starchy potatoes, like Russet in the US, King Edward – UK, or Augusta (mehligkochende Kartoffeln) – Germany.
Use fresh herbs, if available, about 2-3 sprigs of thyme and 1 sprig of rosemary. Chop the leaves finely and discard the stems.