Preheat the oven to 350 degrees Fahrenheit or place a stand on a pan and preheat for 10 minutes
Place parchment paper on a cake pan and grease with baking spray
Firstly take flour, baking powder, and salt to and sieve to get a lump free smooth flour
In a microwave-safe bowl add milk, white chocolate, sugar, and softened butter, microwave for 2 minutes. Microwave till chocolate chips are melted and you see smooth liquid
Add sieved flour, fold and mix. Avoid over mixing
Finally, add sour cream and mix gently until everything is combined well
Transfer the batter and tap the pan to remove air bubbles