Preheat the oven to 350°F (180°C). Line a 12-cup muffin tin with liners.
2. Step
Make the graham cracker crumble: In a medium bowl, mix together the melted butter, graham crackers, brown sugar, and oats until well combined.
3. Step
Make the cupcakes: In a large bowl, mix together the brown sugar and egg with an electric hand mixer on medium speed until combined and smooth, 3–4 minutes.
4. Step
Mix in the vanilla and butter, then the sweet potato, until smooth.
5. Step
Add the flour, baking soda, salt, cinnamon, and nutmeg and beat to incorporate, then add the milk and mix until well combined.
6. Step
Scoop a heaping ¼ cup of batter into each muffin cup, then sprinkle the tops with 1 heaping teaspoon each of graham cracker crumble.
7. Step
Bake the cupcakes for 15–17 minutes, or until cooked through and a toothpick inserted into the center of the cupcake comes out clean. Remove from the oven and let cool completely.
8. Step
While the cupcakes are baking and cooling, make the toasted marshmallow frosting: Add the butter to a large bowl. While whipping continuously with an electric hand mixer on medium-low speed, gradually add the powdered sugar, then the milk, until smooth.
9. Step
Turn the oven to a high broil. Line a baking sheet with parchment paper.
10. Step
Arrange the Kraft® Jet-Puffed Marshmallows in a single layer on the prepared baking sheet. Broil, watching carefully, for 60–90 seconds, until the marshmallows are deeply browned on top.
11. Step
Remove the toasted marshmallows from the oven and immediately fold into the frosting. Let cool completely. If the frosting is still too soft to hold its shape once cooled, place in the refrigerator for 1–2 hours, until firm. Transfer to a piping bag fitted with a large round piping tip.
12. Step
Gently insert the tip of the piping bag through the top of a cupcake into the center and pipe about 1 tablespoon of frosting inside. Then, frost the top of the cupcake and sprinkle with more graham cracker crumble. Repeat with the remaining cupcakes.
