Preheat oven to 180 C
Grease loaf pan with butter/ oil and line with baking paper.
Add oil, butter and sugar in a bowl and whisk well until combined.
Add eggs and vanilla and mix until smooth.
Gently add in flour and buttermilk alternatively until you get a smooth batter.
take out half the batter and mix ½ tsp cinnamon powder in it.
Pour half of the plain batter into the pan, then add dollops of cinnamon batter, then remaining plain batter and finally cinnamon batter.
Swirl both batters together with a skewer.
Bake for 45-50 minutes until toothpick inserted comes out clean.
Stir together brown sugar, caster sugar and cinnamon in a flat bowl.
Take out the loaf after letting it cool in the pan for 10 minutes. Brush melted butter all over and roll the cake in the sugar mixture.
Slice into pieces and serve warm or room temperature.