I love root beer and started thinking about using it in a cake when I came across an old recipe card of my granny’s for a Coca Cola Cake. And then I started thinking about making a really fast cake in the microwave, using the carbonation from root beer to replace the lift that typically comes from eggs. Is it magic — or is it just delicious? Adding some vanilla ice cream really turns it into a whole new version of a root beer float! Root beer can be a pretty versatile ingredient when reduced into a syrup. Add the syrup to nuts for a soda shop-inspired snack, or turn it into a rich ice cream topping with just a hint of chocolate flavor.
For the root beer glazed nuts: Preheat the oven 350 degrees F. Arrange the nuts in a single layer on a baking sheet. Roast, tossing halfway through, until the nuts are fragrant and toasted, 6 to 8 minutes. Remove and allow to cool.
Bring the root beer, cinnamon and kosher salt to a boil in a small saucepan over high heat. Reduce the heat to medium-low and allow to simmer until reduced by half and thickened, about 10 minutes.
Place the toasted nuts in a large bowl and pour the reduced root beer over them. Toss thoroughly to combine; spread out onto a baking sheet, sprinkle with the flaky salt, then allow to cool thoroughly. The glazed nuts can be stored in an airtight container at room temperature for up to 2 weeks. Makes 4 cups.
For the root beer ice cream topping: Bring the root beer, granulated sugar and salt to a boil in a small saucepan over high heat. Boil for 1 full minute, then reduce the heat to a simmer and stir until the sugar and salt dissolve. Stir in the butter, cocoa powder, nutmeg and star anise until completely smooth. Simmer for 5 minutes, stirring occasionally, then pour the root beer mixture into a heatproof bowl or glass measuring cup. Store at room temperature up to 3 days. Makes 1 cup.
For the root beer mug cakes: Stir together the flour, baking powder, cinnamon and salt in a small bowl. Whisk together the root beer and sugar in a second small bowl, then add the oil and vanilla.
Slowly whisk the flour mixture into the root beer mixture until just combined — do not overmix. Divide the batter between two 8-ounce mugs or small microwavable bowls. Microwave until the cake rises and sets, 1 1/2 to 2 minutes. Allow to cool slightly.
To serve, top each mug cake with small scoop of vanilla ice cream, drizzle with the root beer topping and sprinkle with the glazed nuts.