01 - In a stand mixer bowl, combine flour, sugar, yeast, and salt. Mix briefly to distribute evenly.
02 - Add eggs and lukewarm milk to the dry ingredients. Mix on low speed with a dough hook until a shaggy dough forms, ensuring all flour is incorporated.
03 - Increase speed to medium and knead for 5 minutes. Gradually add softened butter, a few cubes at a time, waiting for each addition to absorb before adding more. Continue kneading until dough is smooth, elastic, and pulls away from the bowl sides, approximately 10 minutes.
04 - Transfer dough to a lightly greased bowl, turning to coat all surfaces. Cover with plastic wrap or a damp towel and place in a warm, draft-free area until doubled in bulk, about 1 to 1.5 hours.
05 - Line a 9x5-inch loaf pan with parchment paper, allowing overhang on the long sides for easy removal.
06 - Punch down the risen dough to release air. Turn onto a lightly floured surface and roll into a rectangle approximately 10x16 inches, maintaining even thickness throughout.
07 - Spread raspberry jam evenly over the dough surface, leaving a 1/2-inch border on all edges. If using fresh raspberries, sprinkle them lightly over the jam layer.
08 - Starting from one long edge, roll the dough tightly into a log. Pinch the seam to seal. Using a sharp knife, slice the log lengthwise down the center to expose the layered interior.
09 - Twist the two cut halves together, keeping the cut sides facing up to showcase the swirl. Gently transfer the twisted loaf into the prepared pan, tucking the ends underneath.
10 - Cover loosely with plastic wrap and let rise in a warm place until puffed and noticeably increased in size, about 45 minutes.
11 - Preheat oven to 350°F during the final 15 minutes of the second rise.
12 - Whisk together egg and milk until well combined. Brush the mixture gently over the entire surface of the risen loaf, taking care not to deflate.
13 - Bake for 30 to 35 minutes until deeply golden brown and the loaf sounds hollow when tapped on the bottom. If the top browns too quickly, tent loosely with foil after 20 minutes.
14 - Let cool in the pan for 10 minutes. Using the parchment overhang, lift the loaf out and transfer to a wire rack. Cool completely before slicing for clean cuts.