Preheat oven to 175 °Celsius.
Mix instant coffee powder with hot water. Add to milk and leave aside to cool.
In a separate bowl, beat butter and brown sugar till soft and creamy for approximately 2 minutes. Scrape the sides of the bowl at one-minute interval.
Add eggs, one at a time, beating well after each addition.
In another separate bowl, sift flour, baking powder and salt. Fold in the sifted ingredients into the creamed mixture alternately with the coffee-milk mixture, starting and ending with flour.
Pour half the batter into a well greased and floured loaf tin. Level the top and sprinkle half of the chocolate chunks.
Top with the remaining cake batter and level the top again. Sprinkle with remaining chocolate chunks.
Bake the instant coffee cake for 45 minutes or until a skewer inserted in the center of the cakes come out without any wet batter.
Remove the loaf from the oven and let it cool in the tin for approximately 5 minutes before turning it out onto a wire rack.
Place the loaf facing up and cover it with a kitchen towel. Let it cool slightly before wrapping it with cling wrap and refrigerating it until it has completely cooled down.
Remove the cake from the fridge and unwrap it. Cut and serve as you wish.