Heat the oven to 400°F/200°C. Line an 8-inch/20 cm baking tin with parchment, and brush with butter. Peel and thinly slice the potatoes, then toss in a bowl with the cream to saturate. Pulling the potatoes from the cream, build layers of them in the baking tin, seasoning and scattering over herbs as you go. Brush another sheet of parchment with butter and place it butter-side down on the potatoes. Set another heavy dish on top to weight down the potatoes. Bake until tender, 1 to 1-1/2 hours. Let cool before turning out and cutting into squares or wedges to serve.