Preheat oven to 350 degrees F. Lightly butter an 8-by-4-inch loaf pan; press an 8-inch wide strip of parchment paper into the bottom of the pan so it lines the bottom and long edges, leaving two overhangs on either side.

In a small bowl, whisk together flour, brown sugar, sugar, cinnamon, and salt. Divide mixture in half and set one half aside (this will create the cinnamon sugar swirl inside the cake).

Add cold butter cubes to the other half of the cinnamon sugar mixture. Cut in butter with two knives or a pastry cutter until pieces of butter are no larger than a pea. Add ¼ cup of pecans and work into the mixture with your fingers (reserve remaining pecans) until it clumps together. Refrigerate until ready to use.

In a bowl, whisk together flour, baking powder, baking soda, cinnamon, nutmeg, and salt.

In another bowl, whisk together sweet potato and eggs until evenly incorporated. Whisk in sugar, maple syrup, and vanilla until smooth.

Add sweet potato mixture and melted butter to dry ingredients, and mix until just incorporated and no dry ingredients remain.

Spoon about ⅓ of the batter into the bottom of the prepared loaf pan. Sprinkle with half of the cinnamon sugar mixture and half of the reserved pecans. Spoon another ⅓ of the batter on top, followed by remaining cinnamon sugar and pecans. Spread remaining batter on top, spreading it into a smooth layer.

Sprinkle with refrigerated crumb mixture, breaking it up into pea-sized pieces and keeping the bulk of the crumb mixture ½-inch from the edge of the pan (it will spread as it bakes).

Bake for 55 to 65 minutes or until crumb topping and corners are starting to darken and a toothpick inserted in the deepest part of the bread comes out clean.

Place pan on a wire rack to allow bread to cool completely, 1 to 2 hours. Run a thin knife along the short edges (where there is no parchment), and then use the parchment overhang as handles to gently lift the loaf out of the pan. If it is still warm, let it cool completely on a wire rack before slicing and serving.