Preheat the oven to 350°F/175°C and line and grease a 9x9 inch baking pan.
In a bowl, add the hot butter and chocolate chips. Whisk together until the chocolate has melted and it's well combined.
1/2 cup butter, 3/4 cups semi-sweet chocolate chips
Add in the sugar and continue on whisking.
1/2 cup white sugar
Into a separate bowl whisk the two eggs with a fork until light air bubbles form on the top. This takes about 30 seconds.
Add the eggs, vanilla, and coffee into the bowl and whisk together.
2 eggs, 2 tsp vanilla, 2 tsp instant coffee
Toss in the sifted flour and baking powder and fold using a spatula until just combined. The batter will be runny.
1/3 cup flour, 3/4 tsps baking powder
Pour half the batter into your prepared pan and spread it so it covers the entire bottom. Add 4 of the Kit Kat's on top. Then add remaining batter and spread evenly. The Kit Kat's shouldn't be showing. Scroll up and check out the reference photos for details.
5 Kit Kat
Bake for 22-26 minutes or until a toothpick comes out crumbly. Start checking around the 18 minute mark.