1.Whisk the milk, yeast, and sugar together in the bowl of your stand mixer. Allow the mixture to sit for 5 minutes or until foamy on top. Add the dark brown sugar, butter, vanilla extract, eggs, salt, cinnamon, nutmeg, allspice, and 1 cup bread flour.
2.Using the dough hook, mix on low speed for 30 seconds, scrape down the sides of the bowl with a spatula, then add 2 1/2 cups flour and the currants. Beat on low speed until the dough comes together and pulls away from the sides of the bowl, about 2 minutes. Dough should be a little sticky and soft. If it’s too sticky and not pulling away from the sides of the bowl, mix in additional bread flour 1 tablespoon at a time.
3.Keep the dough in the mixer and beat for an additional 5 full minutes. If the dough becomes too sticky, sprinkle 1 teaspoon of bread flour at a time in the bowl to make a soft, slightly tacky dough. The dough should still feel a little soft. Poke it with your finger, if it slowly bounces back, your dough is ready to rise.
4.Lightly grease a large bowl with nonstick spray. Place the dough in the bowl, turning it to coat all sides in the oil. Cover the bowl with plastic wrap. Allow the dough to rise in a relatively warm environment for 2 hours or until double in size.
5.Grease a 9×13-inch baking pan. Punch the dough down to release the air. Divide the dough into 15 equal pieces. Shape each piece into a smooth ball, pinching it on the bottom to seal. Arrange in prepared baking pan. Cover shaped rolls with plastic wrap. Allow to rise until puffy, about 1 hour.
6.Preheat oven to 350°F. In a small bowl whisk 1/2 cup bread flour and 6 tablespoons water. You want a thick paste that will pipe easily. Add more water, if needed. Spoon paste into a piping bag. Pipe a line down the center of each row of buns, then repeat in the other direction to create crosses.
7.Bake for 20-25 minutes or until golden brown on top, rotating the pan halfway through. If you notice the tops browning too quickly, loosely tent the pan with foil. Remove from the oven and allow rolls to cool for a few minutes.
8.Meanwhile, whisk the powdered sugar and orange juice together. Brush on warm rolls and serve immediately.
9.Cover leftover rolls tightly and store at room temperature for 1-2 days or in the refrigerator for up to 1 week.