Step 1: Grease a 6cm-deep, 23cm (base) square cake pan. Place Edmonds Instant Dry Yeast, Meadow Fresh Milk and 1 tablespoon Chelsea Caster Sugar in a bowl. Whisk to dissolve yeast. Cover. Set aside in a warm place for 10 minutes or until foamy.
Step 2: Sift Edmonds Standard Grade Flour and cocoa into a bowl. Rub in Tararua Butter until mixture resembles fine breadcrumbs. Make a well in centre. Add yeast mixture, egg and remaining Chelsea Caster Sugar. Stir to combine. Turn dough onto a lightly floured surface. Knead for 1 minute. Transfer to a lightly oiled bowl. Cover. Set aside in a warm place for 1 hour or until doubled in size.
Step 3: Punch down dough. Turn onto a floured surface. Knead for 5 minutes or until smooth. Add choc bits. Knead to combine. Roll into 16 balls. Place in prepared pan. Cover. Set aside in a warm place for 30 minutes or until slightly risen. Preheat oven to 200°C/180°C fan-forced.
Step 4: Meanwhile, make paste. Combine Edmonds Standard Grade Flour, Chelsea Caster Sugar and 21/2 tablespoons cold water in a bowl. Spoon into a snap-lock bag. Snip 1 corner from bag. Pipe crosses onto buns. Bake for 10 minutes. Reduce heat to 180°C/160°C fan-forced. Cook for 20 minutes or until golden and cooked through.
Step 5: Meanwhile, sprinkle gelatine over boiling water in a heatproof jug. Stir with a fork until gelatine has dissolved. Place buns, top-side up, on a wire rack. Brush tops with gelatine mixture. Cool. Serve with Tararua Butter.