In a small bowl, melt your butter and add to your cream then set aside
Take your potatoes and grate them on the large slicer side of a boxed cheese grater. This will produce almost completely round thin slices of potatoes.
Shred your gruyere cheese.
This recipe makes two thick layers of the potato and Brussels sprouts together (as one layer).
Start by taking a slice of potato at a time and placing them into your gratin dish just slightly overlapping one another.
Next, sprinkle a thin layer of your Brussels sprouts over top of the potatoes.
Now lightly spoon some of your cream and butter mixture over the Brussels sprouts and potato layer you made.
Sprinkle with your garlic evenly over the top
Now lightly salt and pepper the first layer
Sprinkle ⅓ of your gruyere over all of this.
Repeat the steps above for the next layer until all of the ingredients are used
Top the gratin with the last ⅓ of your gruyere cheese.
Bake for 30 minutes until it is golden on top and the gratin can be pierced easily with the tip of a knife.
Remove from oven and let rest for 5 minutes
This dish can be made mostly ahead of time by preparing all of your ingredients except the potatoes and storing in the refrigerator until you are ready to assemble. The potatoes cannot be prepped ahead of time because they will brown when exposed to air.