1Heat to oven to 450°F. Slice potatoes thinly to about 1/8-inch thickness using a mandolin or food processor. Pat the potato slices dry with a towel.
2In a small bowl, combine the salt, pepper and the garam masala. In another small bowl, have the melted butter ready with a pastry brush. Have all your ingredients ready near your stove top.
3Heat an 8 or 9-inch oven-proof saute pan (or a well seasoned cast iron skillet) over medium heat. Spoon 2 1/2 tablespoons of butter into the pan and swirl to coat. Lay a layer of potatoes, slightly overlapping to cover the bottom of the pan in circular, concentric pattern. Brush with butter over and season with a pinch of the salt/pepper/spice mixture. Repeat adding layers of potatoes, butter and spice mixture until you've used all the potatoes. On top of the last layer of potatoes, brush with butter one last time. By this time, the bottom layer should be busy crisping.
4Carefully cover the pan tightly with a lid or tin foil and bake for 20 minutes. Uncover and bake for another 20 minutes, until the potatoes are beautifully browned and crisp on top and the potatoes are cooked through in the center. Remove from the oven. If necessary, use a spatula to loosen the edges and the bottom layer from the pan. If you want to serve the potatoes in the pan at the table, use a pizza cutter or pair of kitchen shears to cut into 6-8 triangular slices (like a pizza). Or you can invert your potato cake onto a large plate and serve upside down!