Preheat oven to 350 degrees. Line your cupcake pan with liners.
In a large bowl, add in the flour, sugar, cocoa powder, baking soda and baking powder. Whisk together until combined. Set aside.
In a separate large mixing bowl, add in the oatmeal stout, vegetable oil, eggs and vanilla. Whisk until combined.
Add in the sour cream and whisk until all the sour cream is incorporated. Scrape the sides with a spatula.
Add in all of the flour mixture into the wet ingredients. Whisk until most or all of the lumps are out of the batter and the flour is completely incorporated.
Scoop the batter into the prepared cupcake pans.
Place in the oven and bake for 18 minutes or until done. Place a clean toothpick into the center of the cupcakes. If it comes out clean or with moist crumbs, it's done. If it still have batter on it, leave the cupcakes in to bake for a little longer.
Remove the cupcakes from the oven and let cool.
Pretzel Crumb
Preheat oven to 350 degrees.
I placed a couple handfuls of pretzels in a sandwich bag. I crushed them with a rolling pin then measured out my one cup.
Add the crumbs to a mixing bowl.
Add in the granulated sugar and melted butter. Stir until combined.
Add the butter coated pretzels on a shallow baking pan. Place in the oven to bake for 15 minutes.
Remove from the oven and let cool.
Salted Caramel Buttercream
Make your salted caramel sauce and let cool.
Add the egg whites and granulated sugar in a double boiler.
Stir until the sugar is dissolved. This is when the egg whites reach about 115 degrees.
Pour into the stand mixer bowl, and whip with a whisk attachment on high. The meringue needs to come to stiff peaks. If you turn the whisk upside down and the peak stands straight up, you've reached the stiff peak stage.
Add in the sifted powdered sugar and mix until incorporated.
Add in the shortening and butter. Beat until it all comes together. It will thicken up at this point. If the mixture looks like it curdled, keep mixing. It will come back together.
Add the vanilla and mix until combined.
The frosting should be thick and creamy. If it looks separated, keep mixing. It will come back together.
Add in the 1 cup of salted caramel and mix until combined.
Place the buttercream in a piping bag with an 1M tip.
Assemble
The tops of the cupcakes will be sticky. Press the tops of the cupcakes into the pretzels.
Pipe a nice tall swirl on top of the cupcakes.
Drizzle some caramel for garnish using a spoon and flicking it back and forth.
Press a pretzel into the top. Serve!
Notes
To store any leftover cupcakes, with the buttercream icing, you'll want to place in an air tight container and store in the refrigerator for up to 3 days.