Preheat your oven to 350°F (175°C) and grease and flour a 9x13 inch pan or two 8-inch round pans.

Combine 1 cup of mashed sweet potatoes, granulated sugar, and vegetable oil in a large mixing bowl and whisk until smooth.

Add the 4 large eggs one at a time, blending well after each addition, then stir in 1 teaspoon of vanilla extract.

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

Gradually fold the dry mixture into the wet ingredients, mixing on low speed just until combined, then fold in the chopped pecans.

Pour the batter into prepared pan(s) and bake for 30-40 minutes or until a toothpick comes out clean.

Allow the cake to cool in the pan for about 10-15 minutes, then invert onto a wire rack to cool completely.

For the frosting, cream together ¼ cup of softened unsalted butter and ½ cup of mashed sweet potatoes until smooth, then add in 2 cups of powdered sugar.

Once the cake is cooled, frost generously with the prepared frosting using a spatula.