Dissolve the yeast in the 2 tbsp warm water with the ½ tsp sugar. Put the egg yolks, the remaining water and the yeast mixture into the bowl of a mixer and combine. Add the remaining sugar, the butter, salt and half of the flour, and work to a paste. Add the rest of the flour and work until it forms a ball. Turn the dough out of the machine and work by hand, adding more flour if necessary, until the texture is smooth and elastic.
Put the dough into a floured bowl, cover, and leave to rise for several hours until doubled in volume. Line a 30 cm spring-clip cake tin with a column of baking paper to increase its height by 3–4 cm.
Punch down the dough and incorporate the citrus zest and the sultanas (squeezed to remove most of the grappa). Press the dough into the cake tin and leave to rise a second time until it has doubled again in volume. Meanwhile preheat the oven to 160°C/325°F/Gas 3.
Brush the top of the loaf with beaten egg yolk and bake for 45 minutes to 1 hour. The bread is done when it makes a hollow sound when tapped, and when a knife inserted into the centre of the loaf comes out clean.
Use as below, but even better, slice, toast and butter for breakfast.