Preheat the oven to 180°C and grease and line a 30cm x 20cm rectangular baking pan with cooking spray and baking paper.
In a large bowl, cream together the dairy-free butter and caster sugar with an electric mixer until the mixture is light and fluffy and starting to get pale in colour. Add in the vanilla and continue to beat. Gradually add the eggs one at a time, beating the mixture completely after each addition.
In a separate bowl, sift together the flour, baking powder and salt and mix to combine. Slowly add the flour mixture a little at a time, to the wet ingredients, alternating with the dairy-free milk mixing until just combined, being careful not to over mix.
Spoon half of the mixture into another bowl and add in the cocoa powder. Mix until just combined.
Spoon the batter into the lined cake pan, alternating between the chocolate and the vanilla. Smooth down the top and gently drag a knife through the batter, lightly touching the bottom, to create gentle swirls. Place the pan in the oven and bake for 30-35 minutes or until the cake is cooked through and springs back when lightly touched. Let the cake cool in the pan for 10-15 minutes before turning out onto a wire rack to cool completely.
Make the frosting by placing all of the ingredients into a bowl of a stand mixer with the paddle attachment fitter, or use a hand held electric beater to beat everything together until smooth and creamy. If the frosting is too thin, add a little more icing sugar, and if it’s too stiff, add a little more coffee.
Using a flat knife, spread the frosting over the cooled cake. Cut into squares to serve.