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, scraping down the sides as needed.
03 - Increase mixer 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 the dough is smooth, elastic, and pulls away from the bowl sides, approximately 10 minutes total.
04 - Transfer the dough to a lightly greased bowl, turning to coat all sides. Cover with plastic wrap or a damp towel and place in a warm, draft-free area. Let rise 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 later.
06 - Punch down the risen dough to release air. Turn out onto a lightly floured surface and roll into a rectangle measuring approximately 10x16 inches.
07 - Spread raspberry jam evenly over the dough surface, leaving a 1/2-inch border around all edges. Sprinkle lightly crushed fresh raspberries over the jam if desired.
08 - Starting from one long side, roll the dough tightly 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 throughout the twisting process.
09 - Carefully transfer the twisted dough into the prepared loaf pan, tucking the ends underneath. Gently press to evenly distribute within the pan.
10 - Cover the pan loosely with plastic wrap or a towel. Let rise in a warm place until puffed and visibly increased in volume, about 45 minutes.
11 - Preheat the oven to 350°F during the final 15 minutes of the second rise.
12 - Whisk together the egg and milk for the egg wash until well combined. Brush the mixture generously over the entire surface of the risen loaf.
13 - Bake for 30 to 35 minutes, or 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.
14 - Allow the loaf to 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 to prevent the filling from becoming runny.