Preheat oven to 375F.
Grease a baking tin or tray.
Wash potatoes well but do not peel.
Cut a thin slice from the base of each potato so that they will sit flat on a cutting board.
Place a potato on the cutting board and lay a wooden spoon alongside the length of it.
This stops you from cutting right through to the bottom of the potato.
Now, using a sharp knife, held at right angles to the wooden spoon, thinly slice the potato but DO NOT CUT ALL THE WAY TO THE BOTTOM.
Repeat until all potatoes are sliced in this way.
Place potatoes into the baking tin.
Now, using a pastry brush, brush butter or margarine over the top of each potato and use the brush (and your fingers) to carefully push some of the butter down between the slices.
Reserve some butter or margarine to baste during cooking.
Bake for around 45 minutes at 180 degrees-220 degreesC (350 degrees- 425 degreesF) before adding spice mixture.
While the potatoes are cooking, combine the ingredients for the spice topping in a small bowl and mix well.
After 45 minutes, brush the reserved melted butter or margarine over the potatoes then sprinkle the potatoes with the spice mixture.
Return potatoes to the oven and bake for a further 15 minutes or until brown and crispy.
Top with sour cream or yogurt.