[Jamaica] How to cook Spiced Jamaican rolls (bulla)

Ingredients
- 100 g unsalted butter, chopped
- 1 tbsp vanilla extract
- 385 g (1¾ cups firmly packed) brown sugar
- 4 cm-piece ginger, peeled, finely grated
- 700 g (4â…” cups) plain flour
- 1 tbsp baking powder
- 2 tsp baking soda
- ½ tsp ground cinnamon
- sliced avocado, to serve