How to Make It
Stir together orange juice, raisins, and currants in a small microwavable bowl. Cover with plastic wrap; microwave on HIGH until just warm, about 1 minute. Remove and discard plastic wrap. Let mixture cool to room temperature, about 20 minutes. Drain well, reserving 1 tablespoon orange juice for glaze. Set plumped raisins and currants aside.
Place sugar, yeast, salt, orange zest, cinnamon, cardamom, nutmeg, and 4 1/4 cups of the flour in bowl of a stand mixer fitted with a paddle attachment; beat on medium speed until just combined, about 15 seconds. Add warm milk, softened butter, and eggs; beat until a shaggy dough forms, 1 to 2 minutes. Remove paddle attachment from mixer; connect dough attachment. Beat on medium speed until dough is smooth and elastic, about 7 minutes (dough will stick to bottom of bowl but not the sides). Add drained raisins and currants; beat until evenly incorporated, 1 to 2 minutes.
Transfer dough to a large bowl coated with cooking spray; cover with plastic wrap. Let rise in a warm place until doubled in size, about 1 hour.
Turn dough out onto a lightly floured work surface; divide evenly into 12 (about 3 1/2-ounce) pieces; shape into balls. Line a 13- x 9-inch baking pan with parchment paper; coat with cooking spray. Arrange dough balls in prepared pan; cover with plastic wrap. Let rise until doubled in size, 45 minutes to 1 hour.
Preheat oven to 375°F. Whisk together water and remaining 1/4 cup flour in a small bowl until a paste forms. Spoon into a resealable plastic bag; snip a 1/4-inch-wide corner off bag. Pipe a cross on top of each dough ball in pan.
Bake until buns are golden brown, 20 to 24 minutes. Remove from oven. Whisk together jam and reserved orange juice in a small bowl until combined. Brush evenly over warm buns. Using a spatula, remove buns from pan, and transfer to a wire rack. Serve warm, or let cool completely, about 1 hour.
To mix by hand:
Proceed with Step 1 as directed. In Step 2, stir together sugar, yeast, salt, zest, cinnamon, cardamom, nutmeg, and 4 1/4 cups of the flour in a large bowl using a wooden spoon. Add milk, butter, and eggs; stir until a shaggy dough forms. Turn out onto a clean work surface, and knead until dough is smooth and elastic, 8 to 10 minutes. Dough will be very sticky and will smear across work surface for first few minutes until gluten is developed (use a bench scraper to bring dough back into a ball after smearing). Spread dough into a 9-inch circle; pile raisins and currants on top. Fold dough in half to sandwich add-ins; knead until evenly incorporated, 1 to 2 minutes. Continue with Steps 3 through 6 as directed.