Add cake mix, water, eggs, pudding mix, sour cream, vegetable oil, vanilla, and macadamia extract to a bowl.
Use a hand mixer to mix until smooth and well combined.
Measure a 1/4-cup of batter into each liner. Bake at 350°F for 16 to 20 minutes.
Place white baking chocolate in a microwave-safe bowl.
Heat on half power stirring every 15 seconds. After the chocolate melts, let it cool slightly.
Place the butter in a bowl. Use an electric mixer to beat until light and fluffy (about 3 minutes).
Add the cooled chocolate, and mix for an and additional minute.
Add the powdered sugar and vanilla. Mix on low speed until incorporated then switch to medium speed for about a minute to ensure there are no lumps.
Use a spoon, knife, or piping bag to decorate the cupcakes.
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