01 - In a large mixing bowl, whisk together the bread flour, caster sugar, mixed spice, cinnamon, salt, and lemon zest until thoroughly blended.
02 - Add the instant yeast to one side of the bowl, keeping it separate from the salt initially. Create a well in the center of the dry ingredients.
03 - Pour the softened butter, lukewarm milk, and beaten egg into the well. Mix with a wooden spoon until a sticky, shaggy dough forms.
04 - Turn the dough onto a lightly floured surface and knead vigorously for 10 minutes, pushing forward and folding back, until the dough becomes smooth, elastic, and springs back when pressed.
05 - Place the dough in a lightly oiled bowl, turning to coat all surfaces. Cover with plastic wrap or a damp towel and let rise in a warm, draft-free area for 1 hour or until doubled in bulk.
06 - Punch down the risen dough to release air. Turn onto a floured surface and knead in the currants, sultanas, and mixed peel until evenly distributed throughout the dough.
07 - Divide the dough into 12 equal portions. Roll each piece between your palms to form smooth, tight balls, ensuring the surface is taut.
08 - Arrange the buns on a parchment-lined baking sheet, leaving 1 inch between each. Cover and let rise for 45 minutes until puffed and nearly doubled in size.
09 - Preheat the oven to 400°F with the rack positioned in the center.
10 - Whisk the all-purpose flour and water in a small bowl until smooth and thick. Transfer to a piping bag or zip-top bag with the corner snipped.
11 - Pipe a straight cross over each risen bun, applying even pressure to create clean, defined lines.
12 - Bake for 20 to 25 minutes until deeply golden brown and the bottoms sound hollow when tapped. Transfer to a wire rack immediately.
13 - Warm the apricot jam in a small saucepan over low heat until fluid. Brush generously over each hot bun to create a shiny, protective finish.
14 - Allow the buns to cool completely on the wire rack before serving, or serve warm with salted butter for immediate enjoyment.