Preheat the oven to 350°F (175°C) and line about 18 muffin cups with paper liners. Whisk the flour, baking powder, baking soda, and salt together in a medium bowl.

Beat the softened butter, granulated sugar, and brown sugar for approximately 2–3 minutes, until the mixture is light and fluffy. Scrape down the bowl so the butter and sugars combine evenly.

Beat in the eggs one at a time, mixing after each addition, then blend in the vanilla extract. Add the dry ingredients in batches, alternating with the buttermilk, and mix only until combined.

Gently fold or stir in the cream soda without overmixing. Divide the batter among the liners, filling each about two-thirds full.

Bake for 17–20 minutes, until the tops spring back lightly and a toothpick comes out clean or with a few moist crumbs. Cool the cupcakes in the pan for several minutes, then transfer them to a rack to cool completely.

For the ganache, heat the heavy cream until hot but not boiling. Pour it over the butterscotch chips, let it stand for 2–3 minutes, and stir until smooth; allow it to cool and thicken.

Cut a small cone from the center of each cooled cupcake and reserve or discard the cake pieces. Spoon the thickened butterscotch ganache into each cavity without overflowing the tops.

Beat the butter for the frosting until smooth, then add the cooled ganache, vanilla, and salt. Gradually beat in the sifted confectioners' sugar, adding 1–2 tablespoons of milk or heavy cream as needed until spreadable.

Pipe or spread the buttercream over the filled cupcakes. Finish with a drizzle of extra butterscotch sauce or ganache and decorate with butterscotch chips or gold sprinkles if desired.