In a small saucepan, add syrup ingredients and stir to mix. Turn on stove and bring ingredients to a boil over medium heat. Cook until syrup is reduced to half the amount, stirring occasionally to full dissolve the sugar into the champagne. This should take about 3 minutes. You should be left with 2 tablespoons of champagne syrup.
For the cake, combine all ingredients into an oversized microwave-safe mug. Mix with a small whisk until batter is smooth. If desired, pour batter into a 6 ounce champagne coupe glass. Make sure the batter only fills up half of the glass as it will rise further when cooking.
Cook in microwave at full power for about 1 minute. Top of cake should look cooked. Let mug cake cool while making frosting.
To make the frosting: combine frosting ingredients into bowl of stand mixer and whip on high speed until stiff peaks form. Let cake cool a few minutes before frosting top of cake. If you are only making a single cake, you can store the rest of the frosting in the fridge for later use. Cake is best consumed while still slightly warm.
