01 - Preheat oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or generously grease each cup.
02 - In a large mixing bowl, whisk together all-purpose flour, granulated sugar, baking powder, baking soda, salt, and ground cinnamon until thoroughly combined.
03 - Add the cold cubed unsalted butter to dry ingredients and use a pastry blender or fingertips to work the butter into the mixture until a coarse, crumbly texture forms.
04 - In a separate bowl, whisk mashed sweet potato, maple syrup, bourbon, egg, and whole milk until the mixture is smooth and homogenous.
05 - Stir the wet mixture into dry ingredients using a spatula. Mix gently until just combined; avoid overmixing. Dough should be thick and slightly sticky.
06 - Spoon dough evenly into the prepared muffin tin, filling each cup approximately two-thirds full.
07 - In a small bowl, combine granulated sugar and ground cinnamon. Brush muffin tops with melted butter, then generously sprinkle with cinnamon sugar.
08 - Transfer muffin tin to the oven and bake for 20 to 22 minutes until tops are golden and a toothpick inserted in the center emerges clean.
09 - Let muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool slightly before serving.