Anyway,I didn't get the right outcome as I expected from the first try because it's far too overbaked.. So,I decided to have another try and this time was with a little modification..
The recipe (adapted from here)
1 cup plus 2 tbsp all-purpose flour
3/4 tsp baking powder
1/2 scant tsp salt
3 Tbs malted milk powder
100 g unsalted butter
1/2 scant cup brown sugar
1 large egg
1 tsp vanilla extract
1/2 cup malted dark choc balls (Malteser's), coarsely chopped
1/2 cup semisweet chocolate chips
Preheat the oven to 350 degrees. Grease the bottom and sides of a 8*8 inch baking pan and line with parchment paper.
In a medium bowl, whisk together the flour, baking powder, salt, and malted milk powder.
Brown the butter and transfer to a mixing bowl, let cool for 5 minutes then mix in brown sugar whisk until completely combined. Add the egg and vanilla, mix everything until combined.
Fold in the flour mixture, using a rubber spatula, then fold in the malted balls and chocolate chips. The mixture will be very thick.
Turn out into the prepared pan and use an offset spatula to spread it evenly. Bake 18-20 minutes, or until a toothpick inserted in the center comes out clean.
Transfer to a wire rack to cool for 20 minutes. Cut into squares to serve immediately, or they can be stored in an airtight container at room temperature for 3-5 days.