1. Make the dough: In the bowl of a stand mixer, whisk flour, sugar, instant yeast, and salt. Add warm milk and eggs. Mix with dough hook on low until shaggy, then increase to medium until smooth, 3–4 minutes.

2. Knead in butter: With the mixer running, add softened butter 1 tablespoon at a time, letting each piece incorporate. Mix 8–10 minutes more until the dough is glossy and stretchy and passes a windowpane test.

3. First rise: Scrape dough into a lightly greased bowl, cover, and let rise in a warm spot until doubled, 60–90 minutes (or refrigerate overnight for deeper flavor).

4. Make the raspberry filling: In a small saucepan, combine preserves, raspberries, cornstarch, lemon zest, and vanilla. Cook over medium, stirring, until thick and jammy, 3–5 minutes. Cool completely.

5. Shape: On a lightly floured surface, roll dough into a 10×14-inch rectangle. Spread cooled filling over the dough, leaving a 1/2-inch border. Roll up from a long side into a tight log, seam side down.

6. Swirl: Using a sharp knife, slice the log lengthwise to expose layers. Twist the two strands together, keeping cut sides up, then tuck ends under.

7. Second rise: Transfer to a greased 9×5-inch loaf pan. Cover and let rise until puffy and about 1 inch over the rim, 45–75 minutes depending on room temp.

8. Bake: Brush with egg wash and sprinkle with demerara or pearl sugar. Bake at 350°F (175°C) for 30–35 minutes. Tent with foil if browning too quickly. The center should read ~190°F.

9. Cool: Let cool in the pan 20 minutes, then transfer to a rack to cool at least 1 hour before slicing to set the swirl.

10. Serve: Slice and enjoy warm or at room temperature. Excellent plain or with a swipe of soft butter.