Set your oven to 180°C (350°F) and prepare a 9-inch cake pan by greasing it with butter or lining with parchment paper.
Combine plain flour, cocoa powder, baking powder, and baking soda in a large bowl. Sift for a light, airy mix.
Dissolve 2 tbsp instant coffee granules in 80ml hot water, then cool.
In a separate bowl, whisk together natural yoghurt, caster sugar, eggs, and vegetable oil until smooth.
Gradually fold the dry ingredients into the wet mixture, alternating with the mocha coffee, until just combined. Avoid overmixing.
Transfer the batter into your prepared pan and smooth the top with a spatula.
Bake for 35-40 minutes or until a skewer inserted comes out clean.
Allow the cake to cool in the pan for 10 minutes, then turn out onto a wire rack.
Dust with icing sugar or spread with a light coffee glaze for extra indulgence.
Slice generously and serve with a cup of black coffee or a dollop of cream.