To make the crumbles: Preheat oven to 300°F and line a baking sheet with parchment paper.
Combine all ingredients in a medium sized bowl. Use your hands to break the mixture into crumbles and spread them on the prepared baking sheet.
Bake for 10-11 minutes, or until lightly golden brown. (They will harden as they cool).
Let crumbles cool completely. Make sure to break up any large pieces so all crumbles are about the same size. Store in an air-tight container until ready to use.
To make the cake: Preheat oven to 350°F. Line two 12-cup muffin/cupcake pans with 20 paper liners.
Whisk together flour, baking powder, cinnamon, cardamom, nutmeg, ginger, and salt.
Add both sugars, eggs, oil, vanilla, and milk. Mix on medium speed with an electric mixer until all ingredients are incorporated.
Divide batter evenly between cake pans. Bake for 15 to 18 minutes, or until cupcakes are lightly golden brown and set in the center. (Test by inserting a toothpick into the center of each cake layer. If it comes out clean, they're done!)
Let cupcakes cool completely. Once cool, use a sharp knife to cut a little hole in the center of each cupcake. You want the hole to go about halfway down into the cupcake, not all the way through. Spoon peach preserves into each cupcake.
To make the frosting: In the bowl of a stand mixer, cream butter on medium speed until smooth. Add shortening and mix until completely incorporated.
Add peach preserves, vanilla extract, heavy cream, and half of powdered sugar. Mix on low speed until ingredients are mostly combined, and then medium-high speed until completely combined, about 1 minute.
Scrape the sides of the bowl and repeat with the second half of the powdered sugar.
Pipe or spread frosting over the cupcakes. Sprinkle with crumble topping and garnish with a fresh peach slice. (If you’re not serving immediately, you may want to wait and add the peach slices right before you serve them.)
Store cupcakes in a sealed container at room temperature.