Combine the cream, milk, garlic, herbs, 1 teaspoons of salt and 1/4 teaspoons pepper in a medium saucepan. Bring to a low simmer and cook for 30 minutes. Strain, discarding the garlic and herbs and reserve the flavoured cream.
While the cream is cooking, peel the potatoes and cut into thin slices using a mandolin or a sharp knife. Rinse in a bowl of cold water and pat dry with paper towels.
Butter a 10x14 gratin dish with 1 tablespoon of the butter. Arrange one layer of potatoes in the bottom, overlapping by almost half. Sprinkle with a little salt and pepper and pour 1/2 cup of cream over top. Repeat with remaining potatoes and cream, about 4-5 more layers. Dot the top with the remaining butter and cover with foil.
Bake for 45 minutes. Remove the foil and bake for another 15 minutes, until the top is golden brown. Cool for 5 minutes before serving.