Remove the eggs from the fridge to allow them to reach room temperature before adding them to the dough.
Melt 12 tablespoons of butter. Set aside to cool. You want to avoid adding very hot melted butter. Set aside.
Gently warm milk until lukewarm (90-95° Fahrenheit).
Sift flour into a large bowl and combine with salt, lemon zest.
Making The Yeast Dough
Combine dry yeast with 2 tablespoons of sugar and lukewarm milk in a small bowl. Give it a quick stir. Cover the bowl with a dishtowel and keep in a warm place for 15 minutes.
Pour yeast mixture into the flour mixture and begin to beat with an electric mixer (use the dough hook attachment). Add in one egg at a time. Continue to beat until well combined.
Slowly pour the melted butter into the dough. Keep mixing at medium-high speed until all ingredients have been well combined and you have a sticky but smooth dough. Sprinkle the top of the dough with a tablespoon of flour. Cover the bowl with a dishtowel and keep it in a warm place for 1 hour.
Preparing the Dough in the Baking Sheet
Lightly flour a work surface. Use a rolling pin to roll out the dough. Transfer dough to a (9x13) baking sheet. Use your hands to mold the dough into the corners of the baking sheet. Cover with a dishtowel and allow to rest for 30 minutes.
Preheat the oven to 375° Fahrenheit.
Use your index finger to make small indentations all over the dough. Push 12 tablespoons of chilled, chopped butter into the small indentations. Coat the cake with the remaining sugar.
Baking and Adding the 'Moist Maker'
Bake the butter cake for 20-25 minutes or until golden brown. Remove from the oven and immediately pour the heavy cream all over the cake. Allow the cream to soak in and for the cake to cool down. Serve when still slightly warm.
Storing and Freezing
Keep the butter cake in an airtight container. It will stay fresh for about 2-3 days. Bonus tip: if you are serving leftover cake, give it a quick reheat before serving it again. This cake freezes beautifully. Allow the cake to cool completely. Cut it into slices and wrap it in cling film and aluminium foil. Or simply use a an freezer-friendly reusable container.
Tips to making a super light and airy German butter cake:
make sure eggs are at room temperature (take them out of the fridge when you start your baking)
make sure that both the melted butter and warmed milk aren't too hot
slowly pour the melted butter into the dough
make sure you allow the dough to proof (rest and rise) long enough
have no fear with a little bit of patience you'll have the moistest, lightest butter cake imaginable - it's hard, you've got this.