Prepare Butterbeer Reduction: In a medium pot over medium heat, pour 3 cups of butterscotch beer and simmer it until reduced to about ½ cup, which will take 20-30 minutes. Stir occasionally and keep a close eye on it to avoid overcooking. Once reduced, remove from heat and allow it to cool slightly before incorporating into the batter.

Preheat Oven and Prepare Liners: While the butterbeer is cooling, preheat your oven to 350°F (175°C). Line a standard cupcake pan with 24 cupcake liners.

Mix Dry Ingredients: In a large mixing bowl, whisk together 1¾ cups of all-purpose flour, 1½ teaspoons of baking powder, ¼ teaspoon of baking soda, and ½ teaspoon of salt.

Cream Butter and Sugars: In a separate bowl, beat ½ cup of softened unsalted butter, ½ cup of light brown sugar, and ¼ cup of granulated white sugar together using an electric mixer.

Incorporate Eggs and Flavors: Add 2 room-temperature eggs, 2 teaspoons of vanilla bean paste (or extract), and 1 teaspoon of butter extract into the creamed mixture.

Combine Wet and Dry Ingredients: Slowly pour in the cooled butterbeer reduction and ⅓ cup of melted butterscotch chips into the batter while mixing on low speed.

Bake Cupcakes: Divide the cupcake batter evenly among the lined cupcake liners, filling each about two-thirds full.

Make Buttercream: In a large bowl, whip 1½ cups of softened unsalted butter on high speed for 5-10 minutes until it's pale and fluffy.

Prepare Ganache: For the butterscotch ganache, combine ¼ cup of butterscotch chips and 1 tablespoon of heavy cream in a microwave-safe bowl.

Assemble Cupcakes: Once the cupcakes are completely cool, pipe the butterscotch buttercream generously onto each cupcake.