Sprinkle sugar and yeast onto the water and let sit for 10 minutes. The yeast will turn foamy, letting you know its proofed and ready to go.
Melt the butter in a small saucepan over low heat. Stir in the milk, honey, salt, and lemon rind. The mixture should be lukewarm. Remove from heat.
Pour warmed butter mixture into mixing bowl. Stir water and yeast mixture and add to the butter mixture, along with the beaten egg. Beat mixture until well combined. Stir in raisins.
Beat in 2 cups of flour until mixture is smooth. Beat in remaining flour until you have a moist, but not sticky, dough. (If using spelt flour, the dough will be wetter)
Turn out onto a floured surface and knead lightly. Shape dough into a ball and place in oiled bowl. Cover with a cloth and leave in a warm place for 2 hours, or until doubled in size.
Knead dough a few times to release gas bubbles. Shape into 12 evenly-sized buns. Place on greased or parchment-lined baking sheet, leaving room between the buns. Cover and let rise for another hour.
Mix flour, water, and vanilla mixture for crosses. The mixture should be the consistency of a thick glaze, rather than a frosting. If it's too thick, the crosses will crack as the bread rises. If it's too thin, the crosses will disappear as the buns are cooked.
Place in a piping bag, or in a plastic sandwich bag, with a small hole cut in one corner. Pipe crosses over each roll. If the mixture seems thick, add a little water. If it seems thin, add a little flour.
Bake buns in a 375 degree oven for 16 minutes. While buns are cooking, mix milk and honey glaze. After 16 minutes, brush each bun with the glaze.
Return the buns to the oven and cook for an additional 4 - 8 minutes, or until the buns are nicely browned on top, and cooked through. Cool for 10 minutes before eating.
Buns store well in an airtight container. Cover and reheat at 350 for about 5 - 10 minutes.