01 - In stand mixer bowl, combine flour, sugar, yeast, and salt. Mix briefly to distribute evenly.
02 - Add eggs and lukewarm milk to dry ingredients. Mix on low speed with dough hook until shaggy dough forms, scraping bowl as needed.
03 - Increase speed to medium and knead for 5 minutes. Gradually add softened butter cubes, allowing each addition to absorb before adding more. Continue kneading until fully incorporated and dough is smooth, elastic, and pulls away from sides of bowl, approximately 10 minutes.
04 - Transfer dough to lightly greased bowl, turning to coat all sides. Cover with plastic wrap or damp towel. Let rise in warm, draft-free place until doubled in bulk, 1 to 1.5 hours.
05 - Line 9x5-inch loaf pan with parchment paper, leaving overhang on long sides for easy removal.
06 - Punch down risen dough to release air. Turn out onto lightly floured surface and roll into rectangle approximately 10x16 inches.
07 - Spread raspberry jam evenly over dough surface, leaving 1/2-inch border around edges. Sprinkle with lightly crushed fresh raspberries if using.
08 - Starting from long side, roll dough tightly into log. Using sharp knife, slice log lengthwise down center to expose layers. Twist two halves together, keeping cut sides facing up. Gently transfer twist to prepared loaf pan, tucking ends under.
09 - Cover loosely with plastic wrap or towel. Let rise in warm place until puffed and noticeably increased in volume, about 45 minutes.
10 - Preheat oven to 350°F.
11 - Whisk egg and milk until blended. Brush gently over entire surface of risen loaf, being careful not to deflate.
12 - Bake for 30 to 35 minutes until deep golden brown and loaf sounds hollow when tapped on top. If browning too quickly, tent loosely with foil after 25 minutes.
13 - Let cool in pan for 10 minutes. Using parchment overhang, lift loaf from pan and transfer to wire rack. Cool completely before slicing, at least 1 hour.