Dissolve yeast and ½ tsp granulated sugar in ¼ cup of warm water. Stir until dissolved and let sit for a few minutes until a foam starts to form on top. See notes if a foam doesn’t form.
¼ cup water, ½ tsp granulated sugar, 4 g active dry yeast
Sift the flour into a large bowl and make a well. Add the yeast mixture and the rest of the ingredients into the well. Mix until a sticky dough forms and the flour is incorporated. The dough will be very wet and sticky. If it is too wet and doesn’t resemble a dough, add a bit more flour. It will be less sticky after rising.
2 ½ cups all purpose flour, ¼ cup granulated sugar, ½ cup unsalted butter, 1 large egg, 1 tsp pure vanilla extract, ⅓ cup milk, ⅛ tsp sea salt
Cover with a damp cloth and place in a warm area to rise for about 30 minutes, or until doubled in size (see notes).
Prepare loaf pan by lining it with parchment paper and leaving two “handles” to lift out after baking.
Punch down the dough and fold a few times to mix. On a lightly floured surface, and roll out to a 18” by 23” rectangle. Spread the chocolate sesame filling evenly over the dough and sprinkle with chocolate chips. Roll starting from the short side.
¼ cup mini chocolate chips
Cut the sausage in half to make two shorter sausages and in half longwise to reveal the filling. Filling face up, braid the four strands together by twisting and weaving the strands together. Alternatively, you can twist two strands together, twist the other two strands together, and twist both of the larger twists together to make a mega twist.
Carefully lift the babka into the loaf pan and let rise in a warm place (see notes) until it increases by about a third of its size - 30 minutes.
Whisk together the egg and milk to create an egg wash. Brush it over the risen loaf and sprinkle with sesame seeds and flaky salt (optional).
1 large egg, 1 tbsp milk, 1 tsp sesame seeds, Flaky salt
Place the babka into the oven and heat the oven to 180°C (350°F). Bake for 30 - 40 minutes or until the babka is golden brown and feels hollow when tapped. Let cool inside the pan until warm, then lift out and cool on a wire rack until room temperature.