Whisk together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
Place the white chocolate into a microwave-safe bowl, and heat in 20 second intervals until melted and smooth. Add the condensed milk, and mix until combined. The mixture will be quite thick.
Bake for 25 - 30 minutes. Allow to cool completely in the pan on a wire rack before cutting into bars.
Bars stay fresh, stored in an airtight container, at room temperature or in the fridge for up to 1 week. They also freeze well for up to 3 months. Thaw overnight in the fridge before serving.
The calories are an estimate only.