Here’s a sourdough version.
(Final Dough is bakers percentage; Starter & Soaker are straight percentages of the totals in the Final Dough)
Final Dough
Strong White Flour 100%
Starter 118.5%
Butter 45%
Salt 0.7%
Sugar 4.5%
Soaker 82.4%
Starter
Starter 27%
Milk 27%
Quark 19%
Strong White Flour 27%
Soaker
Currents 15.4%
Raisins 21%
Candied Peel 16.5%
Dark Rum 23%
Orange Juice 24.7%
The PArtisan Baker 
Cheers for that Mick! Now, being honest, would you say the baking soda or the sourdough one was actually better? If you can be truly objective of course? 🙂
Objectivity have I none. You’d better make both.
Mind you, you have to admit it’s handy to have an instant rising stollen up your cassock.