01 - Combine flour, sugar, yeast, and salt in the bowl of a stand mixer.
02 - Add eggs and lukewarm milk to the dry mixture. Mix on low speed with a dough hook until a shaggy dough forms.
03 - Increase mixer speed to medium and knead for 5 minutes. Add softened butter gradually, a few cubes at a time, until fully incorporated and the dough becomes smooth and elastic, approximately 10 minutes.
04 - Transfer the dough to a lightly greased bowl, cover with plastic wrap or a clean towel, and let rise 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, ensuring the paper extends slightly over the sides for easy removal.
06 - Punch down the risen dough to release air. Turn 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 the edges. Sprinkle with crushed fresh raspberries if using.
08 - Starting from a long edge, roll the dough tightly into a log. Using a sharp knife, slice the log lengthwise down the center to expose the layered swirl.
09 - Twist the two cut halves together, keeping the cut sides facing upward to showcase the swirl. Carefully transfer the twisted dough into the prepared loaf pan.
10 - Cover the pan loosely and let rise in a warm place until the dough is puffed and fills the pan, about 45 minutes.
11 - Preheat the oven to 350°F.
12 - Whisk together the egg and milk for the egg wash. Brush the mixture gently over the entire surface of the risen loaf.
13 - Bake for 30 to 35 minutes, or until the loaf is deeply golden brown and sounds hollow when tapped on the bottom.
14 - Allow the loaf to cool in the pan for 10 minutes, then carefully remove using the parchment paper overhang. Transfer to a wire rack and cool completely before slicing.