Start by preparing the white chocolate ganache frosting. Heat the heavy cream in a pan or a microwave-safe bowl until hot.

Add the chopped white chocolate and mix until melted into the cream. Reheat the mixture in the microwave in 15-20 second intervals if needed.

Once the white chocolate has completely melted, let the mixture cool a little, then refrigerate to cool completely.

Prepare a 9-inch by 9-inch baking pan by greasing it with oil or butter, then lining it with parchment paper.

Preheat oven to 350ºF

In a large mixing bowl, add the melted butter and brown sugar. Mix until light and fluffy.

Then, add the eggs, one at a time, until fully incorporated.

Next, sift in the flour, baking powder, and salt.

Mix into the batter just until combined, without over-mixing.

Pour the batter into the prepared baking pan.

Bake for 25-30 minutes, until a toothpick poked into blondie comes out clean.

Cool in the pan for 15-30 minutes, then remove it and transfer it onto a wire rack to cool completely.

Remove the white chocolate ganache frosting from the fridge to warm up slightly closer to room temperature.

Whip the frosting using an electric mixer until light and fluffy.

Frost the cooled blondies with the whipped white chocolate ganache.

Sprinkle with cinnamon to finish if desired.