Set the oven rack to the lower-middle position. Preheat to 425°F (218ºC). Lightly grease a 12 cup muffin pan with cooking spray. Place on a sheet pan lined with parchment paper or foil, set aside.
In a medium bowl, whisk together the melted butter, brown sugar, granulated sugar, maple syrup, and salt. Evenly spread the mixture into the bottom of each muffin cup, about 1 tablespoon each. Evenly sprinkle the chopped pecans on top. Set aside.
In a mixing bowl, whisk together flour, granulated sugar, baking powder, baking soda, and salt. Add the buttermilk and ¼ cup melted butter, mix with a spoon until a shaggy dough forms, and the liquid absorbs. Knead dough in the bowl by hand until just smooth, about 30 seconds.
Lightly sprinkle flour on a large piece of parchment paper. This will make rolling easier. Roll the dough out to a 14-inch by 9-inch rectangle.
Brush the surface of the dough with 2 tablespoons (1 ounce) of melted butter.
In a medium bowl, combine brown sugar, cinnamon, and nutmeg. Evenly spread the mixture across the dough's surface, leaving about a ½-inch border along the edges. Sprinkle the chopped pecans evenly on top and lightly press them down.
Starting at the long side, roll the dough into a cigar shape, seam-side down. Use the parchment paper to help lift and roll the dough. Cut into 12 equal portions. Place into each muffin cup, lightly pressing down into the pan.
Place the muffin tin on the parchment paper-lined sheet pan, bake until the rolls have puffed up, dry to the touch, and golden brown, about 16 to 18 minutes. Do not over bake, as the caramel topping can become burnt in flavor.
Gently run a knife along the sides of each bun to make it easier to remove. Immediately place a parchment paper-lined sheet pan on top of the muffin tin, then quickly invert. Let the tin sit on top for 5 minutes, then slowly lift to release the buns from the pan. Scoop out any remaining nuts and sauce and place them on top of the buns. Cool for about 5 minutes, then serve warm.
Storing: Store in an airtight container at room temperature for up to 3 days, or freeze for up to 1 month.
Reheating: Microwave individual pieces on high power in 10 to 15-second intervals until warmed through.