Preheat the oven to 180C (350F) and grease a loaf pan.

In a small bowl, melt the chocolate and water together, stirring until smooth. Set aside to cool slightly.

In a large mixing bowl, add the softened butter and brown sugar and whisk together. Add the eggs, vanilla extract, yogurt, and sourdough starter. Whisk to form a smooth batter.

Add the chocolate mixture and whisk until well combined.

Add the chai tea latte mix, salt, and baking powder to the all purpose flour and mix together.

Gently fold the flour mixture into the liquid batter until well combined.

Pour the mixture into the prepared loaf pan and bake at 180C (350F) for around 50 minutes. Test for doneness by inserting a skewer or toothpick into the middle.

Allow the loaf cake to cool in the tin for around 10 minutes before transferring to a wire rack to fully cool.

To prepare the frosting, add all the frosting ingredients to a food processor or stand mixer and beat until light and fluffy.

Spread frosting over the cooled loaf cake and sprinkle with chopped dark chocolate if desired.