Chocolate hot cross buns

Dough

• 130 g unsalted butter cut into pieces, plus extra to grease
• 200 g milk
• 50 g sugar
• 2 ½ tsp dried instant yeast
• 2 eggs
• 500 g baker's flour plus extra to dust
• 1 ½ tsp ground cinnamon
• 20 g cocoa powder
• 1 tsp sea salt
• 200 g chocolate chips

Piping mixture

• 40 g plain flour
• 50 g water
• 1 tsp extra virgin olive oil
• 1 pinch sea salt

Syrup

• 40 g water
• 40 g sugar