In a large mixing bowl, combine the plain flour, strong white bread flour, caster sugar, fine sea salt, and fast-action dried yeast. Pour in warm whole milk and crack in two eggs, followed by the softened unsalted butter. Mix until the ingredients come together, then knead the dough for about 8-10 minutes until it’s smooth and elastic.

Transfer the kneaded dough to a lightly greased bowl, cover with a clean kitchen towel. Allow it to rise in a warm, draft-free area for 1-2 hours, or until it has nearly doubled in size.

Once the dough has risen, gently punch it down to release the air. Divide the dough into equal portions and shape each piece into small rounds, then flatten slightly to create tart-like buns. Use your fingers to create shallow wells in the center of each bun.

Cover the shaped buns loosely with plastic wrap or a kitchen towel. Allow them to proof for another hour until they have puffed up. During this time, preheat your oven to 375°F (190°C).

Gently brush the edges of the wells with egg wash to promote a golden-brown finish, then carefully fill each well with the prepared coffee custard. Sprinkle the lightly spiced crumb topping around the custard.

Place the filled baking sheet in the preheated oven and bake for 20-25 minutes, or until the buns are golden brown and puffed slightly.

Remove the buns from the oven and allow them to cool slightly on a wire rack. Once cooled, take some grated chocolate and sprinkle it generously over the tops.