Preheat oven and prep muffin tin: Preheat oven to 375f (190c). Lightly brush cups of a 12-cup muffin tin with oil. If you have a 6-cup muffin tin, you can easily make up to 18 stacks. Make number of stacks depending on the number of guests – I estimate 3 stacks per person. Pile stacks high for 12 heaped stacks, keeping in mind they will sink down as they cook.

Make garlic brown butter sauce: Place butter in a small pot set over medium heat. Melt and brown until foaming and sizzling subside, smells nutty, and there are brown bits at the bottom of the pot when you tilt it. Make sure to swirl occasionally and keep a close eye on it to prevent burning. This step takes about 5-8 minutes total time. Stir in garlic, salt, cinnamon, nutmeg and black pepper. Transfer to a bowl to cool. Re-use pot to prepare streusel topping later – no need to wash.

Prepare sweet potatoes: Slice potatoes with skin on or off (I prefer with skin) very thinly 1/16”. I highly recommend using a mandolin to get super thin slices of potatoes in relatively little time. Evenly-thick slices are important for even cooking. If you don’t have a mandolin, slice carefully with a sharp knife. Place sliced potatoes in a large mixing bowl and toss with cooled garlic herb brown butter.

Assemble sweet potato stacks: In each oiled muffin cup, stack potato slices starting with smaller pieces and ending with larger pieces on top. About ⅓ and ⅔ of the way up the stack, sprinkle some grated parmesan. Divide evenly among the cups into heaped stacks. Cover muffin tin tightly with foil.

Bake: Bake in preheated 375f (190c) oven until sweet potatoes are tender but not mushy, about 25 minutes. Check doneness with a wooden skewer – it should slide easily all the way through and back out with just a little bit of resistance. Remove foil and return to bake uncovered until tops are nicely browned, about 15 minutes.

Meanwhile, make pecan bacon topping: Add bacon pieces to small pot over medium heat. Allow fat to render out slowly and bacon bits are crisped up. We want about 1 tablespoon of fat for the streusel. If there is more than that, drain some off. If there is too little, add a bit of neutral oil to make up 1 tablespoon. Separately in a small bowl, mix flour, sugar, maple syrup and salt. Add bacon bits along with the 1 tablespoon of fat, and the chopped pecans, to the flour mixture. Toss well with fork, making sure to maintain little clumps for a crunchy streusel.

Flip stacks and add topping: Once sweet potato stacks are done, remove from oven and lower oven temperature to 350f (175c). Use a small spatula to flip the stacks over by gently pushing down one side enough to grab the other side with tongs to flip. Leave them in the muffin cups, now bottom-side up. Sprinkle streusel topping on top and bake 10 minutes or until streusel is lightly browned. Allow stacks to cool slightly to set, so they can be removed from the muffin tin.

Optional final browning / To reheat for Make in Advance: They can be served straight out of the muffin tin. At this point, they are well roasted with tender middles and lightly browned exteriors. However, I really like to take the browning further with sweet potatoes to draw out the sugars for deeply caramelized edges – the best part of roasted sweet potatoes! The most convenient way is to make this recipe up to this point in advance. Transfer them onto a baking sheet, preferably on a wire rack. This is a great point to hold the Sweet Potato Stacks at room temperature for make-in-advance. To crisp up/reheat, place in a 350f (175c) oven until warm through and browned as desired, about 15 minutes. Tip: watch closely to ensure streusel doesn’t burn – loosely drape aluminum foil on top if there is a risk of burning. Enjoy!