Melt the 10g butter and using a brush, slather it all over a 1½ litre (approx. 6¼ cups or 50¾ fluid oz) cake pan (see note 2).
Pre-heat the oven to 175°C (350℉).
Melt the second amount of butter (100g or ¼ cup + 3 tbsp) butter and set to one side.
Beat the sugar and eggs together until light and fluffy. Add the vanilla.
Combine the flour and baking powder and add to the wet ingredients.
Lastly, add in the butter and milk and mix just until combined.
Mix the brown sugar and cinnamon together.
Pour half of the batter into the prepared pan and sprinkle over the cinnamon mixture.
Using a knife, swirl the sugar into the batter. Pour over the remaining batter.
Bake for around 35-40 minutes, until an inserted skewer comes out clean. Baking times may vary according to the pan you use, so start checking at around 30 minutes.
Leave the cake in the pan until completely cold (it's very soft and a little delicate) and then turn out.
Sprinkle with pearl sugar or powdered sugar. Slice and enjoy!