Ingredients

• Sweet Potato Cake
• 2 ³/₄ cups all-purpose flour
  
• 1 ³/₄ teaspoons baking powder
  
• 1 teaspoon kosher salt
  
• ¹/₄ teaspoon baking soda
  
• 2 teaspoons ground cinnamon
  
• ³/₄ teaspoon ground nutmeg
  
• ¹/₂ teaspoon ground ginger
  
• ¹/₄ teaspoon ground allspice
  
• 1 cup vegetable oil
  
• 1 ¹/₂ cups light brown sugar
  
• 1 cup granulated sugar
  
• 2 teaspoons pure vanilla extract
  
• 3 large eggs
  
• 1 large egg yolk
  
• 2 cups sweet potato purée (from about 1 pound whole potatoes, or canned)
  

• Marshmallow Frosting
• 3 large egg whites
  
• 1 ¹/₂ cups granulated sugar
  
• 1 ¹/₂ teaspoons light corn syrup
  
• ¹/₂ teaspoon cream of tartar
  
• ¹/₄ teaspoon kosher salt
  
• ¹/₄ cup water
  
• 1 teaspoon pure vanilla extract