Makes 9 buns
Sift the flours into a large mixing bowl. Add the salt, superfine sugar, and yeast and stir well.
Combine the milk and butter in a small saucepan and set over low heat until the butter has melted. Do not allow the mixture to simmer; this needs to be done over a low temperature.
Pour the milk and melted butter mixture over the dry ingredients, add the egg and sourdough levain, and stir together to form a soft dough. Grease a large mixing bowl and place the dough inside. Cover the bowl with plastic wrap and set aside to rise in a warm place for about 45 minutes, or until the dough has doubled in size.
Meanwhile, make the filling by beating together the butter, demerara sugar, and cinnamon. Grease your cake pan and line with non-stick parchment paper. Set aside. Place the dough onto a floured work surface and gently roll it out to form an 8 °— 18 in rectangle, approx. 1 in thick (no thinner). Spread the filling evenly over the surface of the dough.
Starting at the longest edge, roll up the dough to form a Swiss-roll shape and cut into 9 slices, approx. 2 in thick. Arrange the buns inside the prepared pan and cover the surface with oiled plastic wrap. Set aside to prove in a warm place for an additional 30 minutes.
Preheat the oven to 350°F.
Brush the tops of the buns with beaten egg, sprinkle over some demerara sugar, and bake for 25–35 minutes, until golden brown. Remove the buns from the pan, without separating them, and set aside to cool on a wire rack for 30 minutes before pulling them apart and diving in. These buns are best eaten on the day they are made.
How to make the levain
3 oz sourdough starter
3/4 cup filtered or mineral water at room temperature
1 2/3 cups organic white bread flour
A levain is the stage between the starter and the bread dough. You take a small quantity of the sourdough starter and activate it. Sourdough levain is what I use in all of my sourdough baking recipes.
Place 3 oz. sourdough starter in a large mixing bowl and stir in the water. Add the flour and mix to a thick paste. Cover the bowl loosely with plastic wrap and set aside at room temperature for at least 4 hours, after which time it will start to bubble. This shows it’s ready to bake with. The levain will remain active for up to 3 days, stored covered in plastic wrap on the kitchen countertop: just make sure you stir it well before use. After 3 days, it will become thin and runny again. At this point, keep back 3 oz to use as a starter for your next batch of levain. (As before, you will need to mix it with 3/4 cup water and 1 2/3 cups flour and then set it aside on the kitchen countertop for between 4 hours and 3 days until needed.)
Excerpted from Fermented: A Beginner's Guide to Making Your Own Sourdough, Yogurt, Sauerkraut, Kefir, Kimchi and More by Charlotte Pike. Photography by Tara Fisher. Kyle Books, 2015.