Preheat the oven to 338°F (170 °C). Prepare an oven dish with baking paper. You're going to need a mixer!
For the starter:
Begin by bringing the water to a boil in a small container on the stove and add the flour. Stir vigorously until the mixture smooths out and the whisk starts to leave trails along the bottom of the container. Remove from the stove and let it cool.
For the dough:
Pour the yeast into the warm milk and leave it for 10-15 min. to activate a little. Put all the dry ingredients into the mixing bowl or use a bowl with a hand blender with dough hooks. Add the yeast, cooled starter, egg, water, rum, lemon rind and vanilla.
Beat for about 4-5 min. with the dough hooks until you get a sticky dough. Without stopping beating, begin adding the cubes of butter at room temperature. Be sure to wait for each cube to get absorbed by the dough well before adding the next one.
Pour the dough onto a floured surface, form it into a ball and put it into a lightly buttered bowl to rise while covered with foil.
Once the dough is ready again, flour the surface once more, transfer the dough to it, knead it again briefly so there's no air bubbles and form it into a long cylinder. Cut it into 24 pieces, shape them into ellipses with your hands and roll them up into scones.
If desired, you can also add a filling. Arrange them onto baking paper and leave them to rise again for 30 min. Smear them with an egg yolk beaten with milk and sprinkle generously with sugar.
Bake at 338°F (170 °C) for about 20-25 min.
Source: Cause It`s Always Delicious!
This unusual starter makes the dough juicier and keeps it soft and fluffy longer. Initially the dough is quite sticky but after it rises it will become stretchy and easy to work with. The filling consists of baking chocolate. Sprinkle the top generously with brown sugar.