The secret ingredient in babka is brioche dough. Kneading is essential to making a beautifully textured brioche. You want a dough that you can stretch between your fingers into a film. This method ensures that your dough will rise well.
In a bowl, cream together the butter, sugar, and egg yolks. Add the salt and milk. Then add the yeast and mix well until the mixture is homogeneous. Add the flour and knead until the dough stretches without tearing (about 10 minutes with a stand mixer, or 50 to 100 folds by hand).
Cover the dough with a cloth or plastic wrap and let it rise in a warm, humid area for about 2 hours. You can also refrigerate the dough overnight. Be sure to take the dough out at least 1 hour before the next step.
Prepare the filling. Melt the white chocolate in the microwave or in a bain-marie. Add the raspberry jam and lemon juice, and mix well. Set aside at room temperature. Grease one or two loaf pans with butter.
Once the dough has risen, flour the work surface and roll out the dough with a rolling pin until it is half an inch (1 cm) thick. Be sure to flour the work surface well, otherwise it can quickly become very sticky. Spread the filling over the dough.
Roll the dough tightly until it reaches 60 cm, and pinch the ends to seal it well. The dough can be used at this full length to make one large babka, or cut in half to make two medium-sized babkas.
Cut the dough lengthwise, making sure that one end remains attached. Twist the dough to form a braid. Place the dough pieces in the bread pan(s). Let rise for 2 hours in a warm, humid area.
Preheat the oven to 350°F (180°C) and bake for 15 to 20 minutes for medium-sized babkas, or 20 to 25 minutes for the larger babka. As it's difficult to determine whether the Babka is ready by sight, we suggest using a probe to check whether it's cooked; the babka is cooked when the middle reaches a temperature of 185°F (85°C).
Leave to cool for 1 hour, then eat immediately. The babka will keep for 2 to 3 days in an airtight container.
