Preheat oven to 350F. Line the bottom of an 8″ square baking dish with parchment paper. In a food processor, mince sweet potato until it reaches a fine rice-like consistency. Then add rest of ingredients (except raisins and carrot). Blend for about 1 minute until smooth. Then stir in grated carrot and raisins. Pour batter into 8″ square cake pan lined with parchment paper and bake on 350F for about 70 minutes until golden on top. You will know it is finished cooking when a knife inserted into the center of the cake comes out clean. Peel and cut sweet potato for the frosting. Place in a small saucepan with about 1-2″ water and cover with a lid. Steam for about 5-10 minutes until soft when poked with a fork. Add steamed sweet potato and rest of ingredients for frosting to food processor and puree for 3-5 minutes until completely smooth. Optional: after pureed, press frosting through a strainer to remove any lumps of remaining lemon zest flakes for a totally smooth result. Chill frosting in freezer in a large metal bowl for about 15+ minutes or until it reaches buttercream frosting consistency and is cooled down. Frost cake as desired and top with chopped pecans (optional, but delicious).