Activate the yeast in lukewarm milk and let sit for 5 minutes until foamy. In a mixer, combine flour, sugar, salt, lemon zest, and vanilla. Add eggs and yeast mixture, then incorporate butter. Knead for 8-10 minutes until smooth.

Place dough in a greased bowl, cover, and refrigerate for 8-12 hours.

Roll out the dough to 12x18 inches. Spread chocolate hazelnut spread, sprinkle chocolate chips, roll tightly, cut in half, twist, and place in a greased loaf pan.

Cover and let rise for 1-2 hours at room temperature. Preheat oven to 350°F.

Bake for 40-50 minutes until golden brown and a toothpick comes out clean.

Prepare sugar syrup by heating equal parts sugar and water until dissolved. Brush over warm babka after baking.

Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.