This Easy Homemade Potato Gratin is the perfect holiday side dish recipe! It's simple to make with only a few ingredients, and it's so creamy!
Preheat your oven to 400 degrees Fahrenheit and prepare a large 9-inch by 13-inch baking dish by spraying it with cooking spray or greasing with butter.
Slice the potatoes and onions into a large bowl using your mandoline slicer. This will ensure you get super thin slices that will bake evenly.
Add the garlic, sage, salt and pepper, milk, and cream to the bowl.
Crumble the beef bouillon cube over the mixture and add the splash of wine.
Use tongs to toss the mixture together until everything is well combined.
Pour the mixture into the prepared baking dish and smooth out the top.
Cover with aluminum foil (or a lid if your baking dish has an oven-safe lid) and bake for one hour at 400 degrees Fahrenheit.
After one hour, remove from the oven and remove the foil or lid.
Sprinkle the Parmesan cheese over the top and return to the oven for another 20-30 minutes, or until the cheese is bubbly and begins to brown slightly.
This recipe can be prepared up to one day in advance and stored in the fridge until ready to bake.