Place all ingredients, including Chelsea White Sugar, in a large mixing bowl fitted with a dough hook and knead until it is smooth and elastic.
Use the stretch test to see if the dough is ready.
Put the dough in a lightly oiled bowl and cover with a shower cap and leave in a warm place to rise for 30 minutes.
Make the filling and the glaze while you wait for the dough to rise.
Filling : Place the butter, Chelsea Soft Brown Sugar, cinnamon and currants in a saucepan and gently melt together over a low heat until the mixture reaches approx. 30°C, stirring occasionally with a spatula.
Lemon & Vanilla Glaze : Put the butter, lemon zest, cream, vanilla and Chelsea Icing Sugar in a saucepan and melt over a low heat to 30°C; give this mixture an occasional stir with a spatula so it doesn't stick to the bottom of the saucepan.
Dough continued : Tip dough onto a lightly floured bench. Using a rolling pin, roll out to a rectangle. Arrange it on the bench so a long edge is facing you.
Brush dough surface with melted butter, then sprinkle the filling evenly over dough (leaving 1cm free at the bottom long edge, so the dough will stick at the seam when rolled up). Wet the edge with water to help it stick.
Starting at the top edge, roll dough towards you, keeping the roll tight and even. Seal at the bottom edge. Lengthen the log to 50cm by rolling it. Using a large chef's knife, cut the roll into 12 even slices, approximately 4cm thick.
Place each dough piece in the greased baking tin with the spiral cut side sitting upwards.
Cover with plastic wrap and leave buns to rise using the indentation test for about 45 minutes at room temperature, until doubled in size and light in texture.
When buns have risen, remove plastic wrap and place trays directly into the preheated oven to bake for 20 to 25 minutes or until golden brown.
Remove from the oven and brush immediately with the glaze. Allow to cool, then serve.