Japanese melon pan with creamy chocolate filling

Ingredients

• 280 g bread flour
• 1 tspn yeast
• 180 ml water
• All the starter dough
• 1 egg yolk + 1 egg
• 120 g bread flour
• 1 tbsp milk powder
• 1/2 tspn yeast
• 4 tbsp sugar
• 1 tspn salt
• 30 g butter
• 200 g Cadbury Milky chocolate ba- r