Preheat the oven to 170 °C. Brush a 22 cm, 2-litre fluted ring cake pan with the melted butter to grease well. Dust lightly with extra flour, tapping out any excess.
1. Place the flour, sugar, butter, eggs, vanilla and milk in a large mixing bowl and beat until combined.
2. Transfer half the mixture to a separate bowl. Mix the cocoa powder, cinnamon and extra milk into a smooth paste and add it to one portion of the batter. Use a spatula or wooden spoon to mix until well combined.
3. Drop alternate spoonful’s of the vanilla and chocolate cake batters into the greased pan and use a butter knife to swirl together to create a marbled effect.