01 - In a stand mixer bowl, combine flour, sugar, yeast, and salt. Mix on low speed to blend evenly.
02 - Add eggs and lukewarm milk to the dry ingredients. Mix on low with a dough hook until a shaggy dough forms, scraping down sides as needed.
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 incorporate before adding more. Continue kneading until dough is smooth, elastic, and pulls away from the bowl, about 10 minutes.
04 - Transfer dough to a lightly greased bowl, turning to coat all sides. Cover with plastic wrap or a clean towel and let rise in a warm, draft-free place until doubled in size, approximately 1 to 1.5 hours.
05 - Line a 9x5-inch loaf pan with parchment paper, allowing overhang on the long sides for easy removal later.
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 around the edges. Sprinkle with lightly crushed fresh raspberries if desired, distributing them uniformly.
08 - Starting from a long side, tightly roll the dough into a log. Using a sharp knife, slice the log lengthwise down the center to expose the layers. Twist the two halves together, keeping the cut sides facing upward to create a decorative swirl pattern.
09 - Gently transfer the twisted loaf into the prepared pan, tucking the ends underneath. Cover loosely and let rise in a warm place until puffy and noticeably increased in size, about 45 minutes.
10 - Preheat oven to 350°F with rack positioned in the center.
11 - Whisk together egg and milk for the egg wash until thoroughly combined. Brush the mixture gently and evenly over the entire surface of the risen loaf.
12 - Bake for 30 to 35 minutes until deep golden brown on top. The loaf is done when it sounds hollow when tapped on the bottom and an instant-read thermometer inserted into the center reads at least 190°F.
13 - Allow the loaf to cool in the pan for 10 minutes. Using the parchment overhang, carefully lift out the loaf and transfer to a wire rack. Cool completely before slicing to prevent the filling from becoming runny.