Make the dough and overnight rise: In the bowl of a stand mixer, add both flours along with the sugar, salt, and dry yeast.
Finely grate the citrus zest directly into the bowl. Pour in the milk, add the eggs and yolks, and include the orange blossom water if using.
Using the dough hook, mix everything by hand just until most of the flour is moistened. Attach the bowl to the mixer and begin mixing on low speed.
Once the ingredients come together into a cohesive mass, increase the speed to medium-low or medium and knead for about 8 minutes, until the dough looks smooth and well developed.
(This dough is rich and soft, so it will remain sticky and will not fully pull away from the sides of the bowl.)
With the mixer running, add the butter gradually, a few pieces at a time, allowing each addition to mostly incorporate before adding more. After all the butter has been added, continue mixing for 3–4 minutes, until the dough becomes more elastic and slightly less sticky.
Cover the bowl and let the dough rest at room temperature for about 1 hour to initiate fermentation. After that, cover tightly with plastic wrap and refrigerate overnight for a slow, flavor-building rise.
Shape the rosca and second rise: The next day, remove the dough from the refrigerator about 1 hour before shaping so it can begin to warm slightly.
Turn the dough out onto a lightly floured surface and gently press it into a rectangle about 5 inches wide and 12 inches long.
Using a rolling pin, roll the dough into a long rectangle approximately 6 x 30 inches, lifting, stretching, flipping, and lightly flouring as needed to prevent sticking.
With the long edge facing you, roll the dough up tightly, as if making cinnamon rolls, gently pulling it toward you as you roll to create surface tension.
When the roll is about halfway formed, place the small figurines evenly along the length, then finish rolling. Pinch the seam firmly from end to end to seal completely.
Transfer the roll to a baking sheet lined with parchment paper or a silicone mat and shape it into an oval wreath. Where the ends meet, make a small indentation in one end, tuck the other end inside, and pinch securely to join.
Cover loosely with plastic wrap and let rise in a warm place (around 80°F / 27°C) until fully doubled in size, about 1 hour, depending on dough temperature.
Prepare the streusel and decorations: While the dough is rising, prepare the sugar topping. In a food processor, combine the butter, sugar, flour, and cinnamon. Pulse until blended, then process until the mixture forms a cohesive ball.
In a small bowl, whisk the egg with 1 tablespoon water to make an egg wash. Set aside with a pastry brush.
Cut the fruit paste into strips about ¼ inch thick and 6 inches long.
Decorate the rosca: Preheat the oven to 350°F (175°C) and place a rack in the center position. Gently brush the surface of the risen rosca with the egg wash.
Using a tortilla press lined with plastic (or a flat plate with two sheets of plastic), flatten a golf-ball-sized piece of streusel into a thin circle about 5 inches wide.
Remove the top plastic, trim the edges into a square, then lift the streusel using the bottom plastic. Peel away the plastic and place the streusel square over the seam of the rosca.
Repeat with three more pieces, spacing them evenly around the wreath. If adding the fruit paste before baking, place the strips between the streusel pieces.
Bake and finish: Place the decorated rosca in the center of the oven and bake until deeply golden, about 25–30 minutes.
Because this is a rich, dense dough, the most reliable way to check doneness is with an instant-read thermometer: the internal temperature should reach 200–205°F (93–96°C).
Transfer the baked rosca to a wire rack to cool completely. If decorating after baking or using candied orange peel, lightly brush simple syrup onto the exposed areas and apply the decorations. Finish with a light dusting of powdered sugar, if desired.