1medium russet potato, peeled and very thinly sliced(about 1.5 cups)
1medium sweet potato, peeled and very thinly sliced(about 1.5 cups)
1cup+ 1/4 cup (100 g + 25 g) shredded cheese, Swiss or Mozzarella
1/4cup(25g) Grated Parmesan Cheese
Spray a 6 x 3-inch round baking pan or a 6 x 4-inch gratin bowl (the first is better for an air fryer the second for the oven)
Place a thin layer of sliced potato on the base
Add a little garlic, thyme, salt pepper and some of the Swiss or Mozzarella cheese
Repeat but the next layer will be sweet potato followed by the same toppings
Then continue until your tin or gratin dish is full
Push down firmly when you add each potato layer to create a nice compact gratin
Finish off with a layer of mixed potato and sweet potato
Pour over the milk
If you are cooking in the air fryer cover with foil and cook at 350F for 40 minutes
If you are cooking in the oven cook uncovered at 350F in the middle of the oven for 55 minutes
When the gratin are cooked the potatoes should be able to be pierced easily with a knife.
Sprinkle over the remaining cheese, Swiss or Mozzarella first then Parmesan.
Either broil on high or place in the air fryer at 400F for 5 minutes.
For the perfect Au Gratin potatoes, make sure you slice all of the potatoes the same size. A mandolin slicer makes this easier.
Add cheese to the top of the potatoes in the final 2-3 minutes of cooking for a cheesy crust.
If you cannot be bother with layering just place all of the ingredients in a large bowl with the exception of the cheese for topping. Then mix well and pour into the cooking bowl and cook as per instructions.
Both mealy and waxy potatoes work well in this recipe, don't be afraid to experiment.