Sweet potato cake layers with toasted marshmallow filling, toasted candied pecans and pecan buttercream.
Preheat your oven to 350 degrees F. Spray three 8-inch or four 6-inch round cake pans with non-stick spray, line with parchment and spray again. Set aside.
In a medium bow, combine the cake flour, cinnamon, baking powder, salt, nutmeg, and ground ginger. Set aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat the sugar and eggs together on medium-high speed until light and fluffy, about five minutes. Add the oil and beat on medium until combined. Add the cooled sweet potatoes and mix until combined. Add the vanilla.
With the mixer on low, gradually add the dry ingredients. Stir until just combined.
Evenly distribute the batter into the prepared pans (about 20 ounces of batter in each of the three 8-inch round pans or 15 ounces of batter in each 6-inch pan). Bake for 30 to 35 minutes, or until a toothpick inserted in the center of the cakes comes out mostly clean.
Let pans cool on wire racks for 10 minutes before inverting cakes onto racks to cool completely.
Place the marshmallows on a cookie sheet lined with parchment paper and sprayed with nonstick cooking spray. Place on the middle rack of the oven, and broil the marshmallows until golden brown on top, about 30-60 seconds. Keep your eye on them!
Remove the pan from the oven and gently turn the marshmallows over and broil them again until they are golden brown on the other side.
In the bowl of a stand mixer fitted with the paddle attachment, combine the butter and powdered sugar and beat on low until blended. Add the vanilla and mix on medium speed for about three minutes.
With the mixer on low speed, add the marshmallow cream and (cooled) toasted marshmallows, and mix for about one minute.
Over medium heat, toast the 2 cups of pecans in the olive oil, stirring frequently. Once toasted, remove one cup of the pecans and cool them on parchment paper.
While the 1 cup of pecans is cooling, add the sugar to the remaining pecans and stir until the sugar is dissolved and is coating the pecans. Pour the sugared pecans over other parchment to cool and use for the filling.
In a food processor, combine the one cup of (non-sugared) toasted pecans with 1 tablespoon olive oil. Pulse until you've created a smooth nut butter.
In the bowl of an electric mixer, fitted with the paddle attachment, beat the butter for about 2 minutes on medium-high speed. This helps to soften the butter without the butter getting too warm by sitting on the counter half the day.
Add your homemade pecan butter. Mix on medium-high speed until well blended, making sure to scrape down the sides and bottom of your bowl.
With the mixer on low speed, gradually add the powdered sugar, followed by the cream. Turn the mixer to medium-high and beat the buttercream for about 3 to 5 minutes.
Place your first cake layer, top side up on a cake board or cake plate. Spread about 3/4 cup of the marshmallow filling over the cake, followed by a generous sprinkle of the toasted pecans.
Place the second cake layer on top of the fillings and layer with another 3/4 cup marshmallow filling and more pecans.
Cover the entire cake with a thin coat of the pecan buttercream. This is your crumb coat. It's not meant to be beautiful, it's meant to be functional - so don't spend a lot of time on this or use too much frosting. You'll freeze the crumb coat for 10 to 15 minutes to lock in the crumbs.
After the crumb coat is set, continue frosting the cake with the remaining buttercream.