In the bowl of a stand mixer fitted with the paddle attachment, combine 1½ cups (188 grams) flour, sugar, salt, and yeast.
In a medium saucepan, heat the milk, ½ cup (120 grams) water, and butter over medium heat until warm but not hot—about 120°F–130°F (49°C–54°C). The butter should be melted, and the mixture should feel warm to the touch.
Add the warm milk mixture to the flour mixture and beat on medium speed until combined. Add the egg and beat again until incorporated. With the mixer on low speed, gradually add 2 cups (250 grams) flour until a shaggy dough forms, stopping once or twice to scrape down the sides of the bowl.
Switch to the dough hook attachment. Knead on low speed until the dough becomes soft and slightly sticky, about 6–7 minutes, stopping occasionally to scrape down the hook and bowl.
Add up to remaining ¼ cup (31 grams) flour, 1 tablespoon (8 grams) at a time, if dough is too sticky. Turn out dough onto a lightly floured surface, and shape into a smooth round.
Lightly oil a large bowl. Place dough in bowl, turning to grease top. Cover and let rise in a warm, draft-free place (75°F/24°C) until doubled in size, 40 minutes to 1 hour.
When the dough has doubled in size and passes the finger dent test, turn it out onto a lightly floured surface and roll it into a large rectangle (about 20" × 15").
Spread the boysenberry preserves evenly over the dough, leaving a small border around the edges to prevent leaking.
Starting at a long edge, roll the dough tightly into a log. Using a sharp knife or bench scraper, cut the log lengthwise down the center, stopping about 1 inch from one end so the two halves remain attached.
Twist the two pieces together, keeping the cut sides facing up.
Coil the twisted dough into a spiral and place it in a parchment-lined springform pan. Cover loosely and let rise until puffy, about 30–45 minutes.
Preheat oven to 350°F.
Bake for 45–55 minutes, until deeply golden. Tent loosely with foil if browning too quickly. Cool to room temperature before slicing.