Preheat your oven to 160 C / 325 F.Grease and flour an 8 inch round pan well. Line the bottom with parchment (optional)
Mix the coffee powder into the hot water. Keep aside.
Whisk together the flour , baking soda and salt. Keep aside.
Melt the butter and chocolate (chopped) together in the microwave or in a double boiler on the stovetop until smooth.
Mix in the coffee and then the sugar into the chocolate-butter mixture.
Whisk in the dry ingredients.
Whisk in the eggs and vanilla until incorporated.
Pour into prepared pan and bake at 160 C/ 325 F for 45-50 minutes until a toothpick inserted in the centre comes out clean and the top springs back lightly when touched.
Cool in pan for 15 minutes and then invert out carefully to cool completely right side up on a wire rack.
Notes
Store cling wrapped at room temperature for a day or chilled for 3 days .