Preheat your oven to 180c (350F) / 160c fan. Line an 8x8 inch baking tin with baking paper. (If you scrunch it up first, its much easier to push into the corners)
Sift together flour, malted milk powder, baking powder then add sugar. Mix well so everything is distributed.
Add the mlted butter, maple syrup and vanilla and mix a little, then add the beaten eggs and mix until fully incorporated. Add the chocolate chips and mix to distribute evenly.
Pour the batter into the prepared baking tin and spread to the edges an into the corners.
Bake in the oven for 25-30 minutes until the edges are firm but the middle is still soft (there should only be a slight wobble when you shake the pan). Cool in the tin before frosting.
For the buttercream;
In the bowl of a stand mixer, beat the butter on medium adding the icing sugar 1 tablespoon at a time until it is all incorporated. Beat on high for another minute or two until light and fluffy. Scrape down the sides of the bowl as necessary.
Add the malted milk powder and beat until incorporated. Then add the cream and beat for another 2 minutes on high making sure to scrape down the sides of the bowl as necessary.
Spread over the blondies, then slice into 16 pieces.
It’s always best to weigh out your ingredients, but if you don’t have a kitchen scale, then measure things like flour and cocoa by using the spoon and level method. Don't use your cup to scoop out of the flour container as you will end up with too much. Instead, spoon it into the cup measure, then level off with the back of a knife. Don’t tap it down to flatten it as, again, you’ll end up with too much.