Heat the oven to 400°F. Scrub the sweet potatoes, prick them with a fork, and place them on a sheet pan. Roast for 45 to 50 minutes, or until a fork slides in easily.

Scoop out the sweet potato flesh and mash it until smooth. Then let it cool completely.

Lower the oven to 350°F and grease three 8-inch round pans with baking spray. Toast the pecans on a sheet pan for about 5 minutes, then let them cool.

Sift the flour, both sugars, cinnamon, baking powder, baking soda, salt, nutmeg, and ginger into a large bowl.

In another bowl, whisk the cooled sweet potato with the oil, vanilla, and eggs.

Add the dry mixture to the wet ingredients a little at a time on low speed until the batter is smooth.

Divide the batter evenly among the three pans. Bake for 20 to 25 minutes, or until a toothpick comes out clean.

Cool the cakes fully in the pans, then turn them out onto a rack.

Beat the cream cheese, butter, and vanilla for about 2 minutes. Gradually add the powdered sugar and cinnamon, then thin with heavy cream one tablespoon at a time until spreadable.

Frost the first layer and scatter 1/3 cup pecans over it. Repeat with the second layer.

Add the third layer, frost the top and sides, and press the remaining pecans onto the sides. Dust with cinnamon, then refrigerate for at least 4 hours before slicing.