Caramelized Apple-Ginger Cake

Ingredients

• cooking spray (as needed for pans)
• ½ cup coarsely chopped, toasted walnuts
• ½ cup granulated sugar
• ½ cup water
• 9 tablespoons unsalted butter (at room temperature, divided)
• 2 crisp, tart apples (peeled, cored and cut into ½‑inch dice)
• ½ cup packed brown sugar
• 1 large egg
• ½ cup unfiltered molasses
• 1 2/3 cup all-purpose flour
• 1 teaspoon baking powder
• ½ teaspoon baking soda
• 1 ½ teaspoon powdered ginger
• ½ teaspoon powdered cinnamon
• ½ teaspoon kosher salt
• ½ cup buttermilk
• 12 dried apple rings (optional, as garnish)
• 2 teaspoons cinnamon-sugar (optional, as garnish)
• mint leaves (optional, as garnish)