4Thinly slice the sweet potatoes into rounds, approximately 3mm (1/8 inch) thick.
5Brush the inside of the muffin tin cups with melted butter.
6Combine the remaining melted butter in a large mixing bowl with the rosemary, garlic, salt, and pepper.
7Toss the potato slices in the butter mixture until well coated.
8Place one sweet potato slice in each cup of the muffin tin.
9Toss the remaining potato slices with parmesan until well coated.
10Stack the seasoned sweet potato slices in piles in each muffin tin cup.
11Brush any remaining butter/parmesan mixture from the bowl over the stacks. If the leftover parmesan is clumpy, loosen it with a dash of oil.
12Cover the muffin tin with foil and bake for 35 minutes.
13Remove the foil, increase the oven temperature to 200C/400F, and bake for a further 15 minutes, or until lightly charred and soft through the center.
14Carefully scoop out the stacks using a spoon and drizzle/brush with any butter remaining in the tin.
Try to get fresh, dusty parmesan or use a coarse grater for a block of parmesan.
Parmesan adds a deeper savory/salty flavor that balances the sweetness of the potatoes, but you can omit it. If omitted, the garlic flavor will be more prominent, and consider adding 1/4 tsp more salt.
Check if the sweet potatoes are soft right through the center with a butter knife.