• Preheat the oven to 350°F or 180°C (170°C for fan assisted ovens).
• Put the instant coffee in a small bowl and add the boiled water. Stir together well and set aside to cool a bit more. (If using perked coffee or espresso, measure 2 tablespoons and set aside.)
• Grease a 2 pound (123cm x 12cm x 13 cm) loaf pan with a bit of the extra butter. You can also line the cake pan with greaseproof paper at this stage if you like. I generally just grease the pan.
• Beat the butter, brown sugar and caster or granulated sugar together in the large bowl of an electric mixer until thick and pale.
• Add the eggs, one at at time, beating well after each addition.
• Sift the flour and baking powder together in a medium bowl.
• With the electric mixer on low speed, use a large spoon to add the flour and baking powder to the mixture in the bowl of the electric mixer a bit at a time. When the flour is all added, blend together thoroughly with the electric mixer.
• Stir the milk into the instant coffee and add it to the batter, combining thoroughly.
• Beat the batter until it is smooth (about 1 minute) and then remove the bowl from the electric mixer.
• Stir in the chocolate chips with a wooden spoon.
• Transfer the batter to the greased loaf pan and bake for 35 to 45 minutes, or until a skewer inserted in the centre of the cake comes out clean. This may take more or less time, depending on your oven so be sure to keep an eye on the cake as it bakes.
• When the cake is done, remove the pan from the oven and place it on a wire rack to cool for 15 to 20 minutes.
• Then turn the cake out on to the wire rack and allow to cool completely.
• When the cake is completely cool, make the glaze.

To make the glaze:

• Put the icing sugar in a medium bowl.
• Add the water, a bit at a time, blending thoroughly after each addition, until a drizzle-able consistency is reached. You may need a bit less or a bit more water.
• Drizzle half the glaze over the cake. Set the remaining glaze aside.
• Sprinkle a few of the additional chocolate chips over the top, pressing them gently into the wet glaze if you are having trouble getting them to stick.
• If you have time, let the glaze and chocolate chips set for about half an hour. However, if time is tight you can carefully proceed to the next step.
• Drizzle the remaining glaze over the top so that it looks pretty. Don't worry if you have some left over.
• Let the glaze set for at least 10 minutes before serving.