Sweet sourdough buns with filling

Delicious, rich, sweet burgers. Eat such a bun, preferably two or three, and life seems fuller.
*****************************************
Ingredients:
For dough:
80 g wheat starter starter, 50% moisture
80 g wheat flour of the highest or 1 grade
40 ml water
OR
50 g wheat starter starter 100% moisture
110 g wheat flour of the highest or 1 grade
40 ml water
For the test:
all dough
350 g flour
140 ml water
1 egg
30 ml vegetable oil
1 tbsp sugar
½ tsp salt
For filling:
any sweet filling to taste