Prepare the Raspberry Filling
Mash raspberries with sugar and lemon juice.
Cook briefly to thicken if desired, then cool completely.
Make the Brioche Dough
In a large bowl, combine flour, yeast, sugar, eggs, milk, and salt until a sticky dough forms.
Gradually incorporate softened butter, kneading until smooth and elastic (8–10 minutes by hand or 5–6 minutes in a stand mixer).
First Rise
Cover dough and let rise in a warm place until doubled, about 1–2 hours.
Shape and Add Raspberry Swirl
Roll dough into a rectangle.
Spread raspberry filling evenly over the dough.
Roll into a tight log and place in a greased loaf pan. Optionally, braid or twist for a decorative look.
Final Proof
Allow shaped dough to proof until slightly puffy, 45–60 minutes.
Bake
Preheat oven to 350°F (175°C).
Brush with egg wash and bake 30–40 minutes until golden brown and cooked through.
Let cool slightly before slicing to maintain swirl structure.