For the cake batter: Preheat the oven to 350 degrees F. Line a standard muffin pan or cupcake pan with 12 cupcake liners.
In a pot, heat the butter and stout over medium heat until the butter is melted. Remove from the heat, add the cocoa powder and whisk until the mixture is smooth. Set aside to cool slightly.
In a medium bowl, sift together the flour, granulated sugar, baking soda and salt and whisk to blend. Set aside.
Using a stand mixer, beat the sour cream and egg together in a large bowl to blend. Add the stout/chocolate mixture and beat just to combine. Add the flour mixture and mix on a low until just combined.
Divide the batter among the cupcake liners, filling them three-quarters full. Bake until a tester inserted into the centers comes out clean, about 17 minutes. Cool the cupcakes on a rack completely.
For the beer syrup: In a pot, combine the granulated sugar and stout and simmer together until the sugar is completely dissolved. Remove from the heat and stir in the vodka. Set the mixture aside to cool.
For the stout filling: Using a stand mixer, beat the confectioners' sugar and butter together until well combined. Add the stout, vanilla extract and salt and mix until creamy.
For the rocky road frosting: In a clean metal bowl of a stand mixer, whisk the granulated sugar and egg whites together over a pot of simmering water. Whisk occasionally until a candy thermometer inserted in the mixture registers between 140 and 160 degrees F (or until you can't feel the sugar granules when you rub the mixture between your fingers).
Transfer the mixture to the stand mixer and using the whisk attachment, whip until the mixture turns white and almost doubles in size, and the outside of the bowl feels at room temperature. Add the vanilla and salt and continue to whisk.
Switch the attachment from a whisk to a paddle and at a low speed, add the butter a few tablespoons at a time and continue mixing. The frosting is done when it looks glossy and smooth. Stir in the chocolate. Fold in the mini marshmallows and slivered almonds with a rubber spatula.
To assemble: Brush the beer syrup onto the cupcakes with a pastry brush, or drizzle over the cupcakes using a spoon. Allow the cupcakes to absorb the syrup. Cut a small and shallow hole in each cupcake, and fill each hole with some of the stout filling. Using an ice cream scoop, scoop some rocky road frosting onto each cupcake.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.