Combine the yeast, 1 tsp sugar, and warm water in a small bowl and let sit for 5 minutes until foamy—this confirms your yeast is alive and active. In a large mixing bowl, combine the warmed milk, oil, 1/4 cup sugar, salt, cinnamon, nutmeg, orange zest, and lemon zest. Pour in the activated yeast mixture and stir to combine. Add 1 cup of flour and mix until no dry flour remains. This creates the foundation for flavor development, with the spices and zest fully incorporated into the wet ingredients from the start.
Add 2 cups of flour to the wet mixture and use an electric mixer with a dough hook to knead for 2-3 minutes. The dough will be shaggy at this point. Add the remaining 1 cup of flour in 1/2 cup increments, mixing between each addition, until the dough pulls away from the sides of the bowl and is slightly tacky but not sticky. If the dough seems too wet, add the remaining flour incrementally—you want it soft and pliable, not stiff.
Continue kneading the dough on medium speed for about 4 minutes until it becomes smooth and elastic. During the last minute of kneading, add the raisins and currants, allowing them to be fully distributed throughout the dough. The fruit should be evenly scattered so each bun gets a good amount. I like to reserve a few raisins to press into the tops of the shaped buns for a prettier presentation.
Transfer the dough to a lightly oiled bowl, turning it to coat all sides. Cover with a damp towel or plastic wrap and let rise in a warm place for 1 hour until doubled in size. While the dough rises, line a 9x13 inch baking pan with parchment paper. After the rise, punch down the dough gently to release excess air, then divide it into 12 equal pieces. Roll each piece into a smooth ball and arrange them seam-side down in the prepared pan, spacing them close enough to touch slightly.
Cover the pan of buns with a damp towel and let them rise for 30 minutes until puffy and almost doubled. While they rise, preheat your oven to 375°F. In a small bowl, whisk together 1 tbsp maple syrup and 2 tbsp milk to create a glaze. Once the second rise is complete, brush the glaze generously over the tops of each bun—this will give them a beautiful golden shine and subtle sweetness.
Bake the buns at 375°F for 20 minutes until golden brown and a toothpick inserted into a bun comes out clean. Remove from the oven and immediately transfer the buns to a cooling rack. Let them cool completely—at least 30 minutes—before piping on the icing crosses. This cooling time is important because the buns will continue to set and the icing will adhere better to a room-temperature surface.
Once the buns have cooled completely, make the icing by whisking together the sifted powdered sugar, 1/4 tsp vanilla essence, and 2 tsp milk until smooth and pipeable. If the icing is too thick, add milk a few drops at a time; if too thin, add more powdered sugar. Transfer the icing to a piping bag fitted with a small round tip and pipe crosses on the top of each bun. I prefer to pipe thin, delicate lines rather than thick ones—they look more elegant and professional.