Activate the yeast by combining warm milk, yeast, and a pinch of sugar. Let sit 10 minutes until foamy.
Mix the dough in a stand mixer with flour, sugar, and salt. Add eggs and yeast mixture on low until a shaggy dough forms.
Add butter one piece at a time on medium speed. Mix 8 to 10 minutes until smooth and elastic.
First rise: Place dough in an oiled bowl, cover, and let rise 1.5 to 2 hours until doubled.
Make the filling by cooking raspberries, sugar, and cornstarch over medium heat for 5 minutes until thick. Cool completely.
Roll the dough into a 30x20cm rectangle. Spread cooled filling evenly, leaving a 2cm border.
Shape the loaf by rolling dough into a log, slicing lengthwise, and twisting the two strands together cut-side up.
Second rise: Place in a greased loaf pan, cover loosely, and proof 45 to 60 minutes until puffy.
Bake at 175°C (350°F) for 30 to 35 minutes. Brush with egg wash before baking. Tent with foil if browning too fast.
Cool in the pan 15 minutes, then transfer to a wire rack. Wait at least 30 minutes before slicing.