In the bowl of your stand mixture combine 3-4 tablespoons warm milk (not hot, or you’ll kill the yeast!), a pinch of sugar, a tablespoon flour and the yeast. Mix to combine and wait for it to foam (about 5-10 minutes)
Add the rest of the milk, 2 ½ eggs (break the third egg into a glass, beat it and pour half of it into the bowl), and the rest of the ingredients. Using the dough attachment knead for 15 minutes.
Let the dough rest in a warm place until doubled in volume (2-4 hours depending on the temperature mostly).At this step you can make the babka or refrigerate overnight for the best texture and flavor.
In the meantime, make the filling: transfer in a small bowl the goji berries, white sugar and hot water and let stand for 10 minutes. Then blend in a blender until smooth.
In a double boiler or in the microwaves, melt the white chocolate and add the goji berry mixture, brown sugar, saffron and cinnamon. Mix well and leave to cool.
Line with baking paper two baking tins, about 9x5 inch (24x12 cm)
Divide the dough in two and roll out into rectangles with their short side the same length as the length of your baking tins.
Spread the filling onto the rectangles, roll into logs and cut them lengthwise.Form braids and place them inside the tins.Cover with a clean towel and put them in a warm place until double in volume (it may take from half an hour to 2 hours)
Preheat your oven at 350°F (175°C) about 15 minutes before baking them.
Beat the reserved half egg with one tablespoon milk and a pinch of sugar, and gently brush each babka.
Bake for 30-40 minutes or until a toothpick inserted at the center comes out clean.Let them cool for 10 minutes and invert onto a rack to cool completely. Eat!
Notes
After the first rise, the dough can be stored in the freezer for one month or even longer. Just thaw it overnight in the refrigerator, form the breads and continue normally.