Heat milk in a small saucepan to 110 degrees F (43 degrees C). Pour milk into a large bowl; whisk in ½ cup flour and yeast. Cover the bowl with plastic wrap; set aside until bubbly, about 15 minutes.

Place 1 ⅔ cups flour, ⅓ cup white sugar, salt, cinnamon, cloves, ginger, and nutmeg in the bowl of a stand mixer fitted with the paddle attachment; beat on low speed for a few seconds to combine. Add ¼ cup butter; beat on low speed until incorporated, about 2 minutes.

Add yeast mixture and egg to flour mixture; beat on low speed for 2 minutes. Stop the mixer; rest for 10 minutes. Beat on medium speed until smooth and elastic, about 2 minutes. Beat in currants and citron on the lowest speed until evenly distributed, about 1 minute.

Grease inside of a large bowl with butter; place dough in bowl, turn to coat dough with butter on all sides. Cover the bowl with plastic wrap; let dough rise in a warm place until doubled in volume, about 1 hour.

Line a baking sheet with parchment paper; set aside. Turn dough out onto a lightly floured surface; pat into a rough square, and cut into 12 equal pieces. Form each piece into a round bun; place on the prepared baking sheet. Press a cross pattern into each bun with the back of a knife; cover buns with a damp cloth and allow to rise until doubled in volume, about 45 minutes.

Preheat the oven to 375 degrees F (190 degrees C).

Bake buns in the preheated oven until deep golden brown, about 15 minutes.

Meanwhile, bring 2 tablespoons white sugar and 1 tablespoon water to a boil in a small saucepan. Remove buns from the oven. Transfer buns on parchment paper to a wire rack; immediately brush buns with white sugar glaze. Cool buns completely, about 20 minutes.

Combine confectioners' sugar and 2 teaspoons water in a small microwave-safe bowl. Microwave icing mixture until smooth and warm to the touch, about 10 seconds. Place icing mixture in a resealable plastic bag, snip off one corner of the bag, and pipe a cross over fully cooled buns; set aside for icing to dry, 30 minutes.