1 Preheat oven to 350 °F (180 °C). Grease a 1.5lb loaf tin with a little unsalted butter.
2 Start by making the cake. In a medium sized bowl, cream together butter and caster sugar until light and fluffy. Now crack in the eggs one at a time, mixing after each addition.
3 In a separate small bowl, mix together the flour and baking powder before adding to the wet ingredients. Now, add the vanilla essence and yoghurt to the mixture and fold together until combined.
4 To make the cinnamon sugar, sieve the brown sugar into a small bowl and mix with the ground cinnamon.
5 Sprinkle 1/3 of cinnamon sugar into the greased loaf tin, making sure you cover the sides as well as the base. Now, pour half of the cake mixture into the loaf tin, spreading it out into an even layer, and sprinkle with 1/3 of the cinnamon-sugar. Pour the remaining mixture on top and use a skewer or knife to swirl through the batter a few times. Finally, sprinkle the remaining cinnamon-sugar all over on top.
6 Bake for 45-50 minutes, until a toothpick inserted in the center comes out clean*. Allow the cake to cool for 10 minutes in the pan before removing to a wire rack to cool completely.
7 To make the glaze, mix the icing sugar and milk together and drizzle over the top of the loaf. Cut into 10 slices and serve. The cake will keep in an airtight container for up to 1 week.
*Cover the cake with tin foil after 35 minutes to stop the top from browning too much.