Prepare coffee: Make the instant coffee and let cool to room temperature. (putting it in the fridge helps to cool it quickly)
Preheat oven/prepare tin: Line a 22 cm springform tin with baking paper on the bottom, and grease the sides of the tin with butter. Preheat oven to 175 degrees C or 350 degrees F.
Mix Dry Ingredients: In a large mixing bowl, mix together the flour, baking powder, salt and cocoa powder.
Whisk Eggs: Use a whisk to beat together the eggs, granulated sweetener and vanilla until fluffy and pale. Hand whisk for about 1 – 2 minutes o make sure sweetener is dissolved.
Add Wet Ingredients to eggs: Melt butter in microwave and to the egg mixture, along with the sour cream and cooled instant coffee. Whisk vigourously until all the lumps are gone and it is smooth, silky and a caramel like colour. (about 2 minutes or so)
Combine Dry and Wet Ingredients: Make a well in the centre of the dry ingredients and pour in wet ingredient mixture. Use a spatula to mix through, making sure to blend in all the flour. Set Aside.
Melt Chocolate: Microwave chocolate until its only just melted (suggest microwaving at 50% power in 30 second spurts until it reaches that “just melted”stage)
Pour Chocolate and Milk into Batter: Add the melted chocolate, along with the milk to the cake batter and gently stir through with spatula to create a thick dark batter.
Bake: Bake for 30 minutes. To test if cake is cooked, insert a skewer into the centre. If it comes out clean, almost clean with few crumbs, cake is cooked. Let cool on a wire rack before slicing. Store in an air tight container at room temperature for 3 to 4 days.