Preheat oven to 220°C. Grease a dish with some of the butter and reserve the rest of the butter for later.
Place Gruyere into the Thermomix bowl. Grate 4 sec/speed 8. Pour into a small bowl and set aside.
Place garlic into the Thermomix bowl. Chop 3 sec/speed 6. Add cream. Warm 5 min/70°C/speed soft. Set aside to infuse.
Pat dry potatoes with paper towel.
Layer one third of the potatoes on the bottom of the dish. Top with a third of the cheese, salt and pepper. Continue until you've used up everything. Finishing with cheese.
Strain the garlic out of the cream and discard. Pour infused cream over the Dauphinoise.
Dot the top with remaining butter. Bake, covered in foil for 20 minutes. Remove foil and continue baking for 25-30 minutes.