In the bowl of the mixer, add the yeast, 1 tablespoon of sugar and warm water. Mix lightly and cover with a dish towel for 10 minutes for yeast to activate 

Add the sugar, egg, oil, flour, and salt and mix using your dough hook on medium speed until the dough comes together. If dough is too liquid or too sticky, add more flour, 1 tablespoon at a time

When dough comes together and is soft and elastic (about 10 minutes), remove from mixer and place in a greased bowl. Cover with a dish towel and let it rise for 1 1/2 hours (or until doubled its size) in a warm area

In the bowl of the food processor, add the pistachios and sugar and process until fine

In a small saucepan, add the chocolate, butter and milk. Mix on low heat until the chocolate and butter melts

Add the chocolate mixture into the food processor and process until creamy

Cool in the refrigerator until ready to use

Divide the dough into 6 equal portions and shape into balls. Cover with a dish towel and let them rest for 20 minutes

Take one ball and roll into a narrow rectangle. Using a spoon or brush, add some of the creamy filling all over, then sprinkle the chopped pistachios on top 

Roll this strip into a log (it will be a bit messy),  and repeat this step with the other 5 dough balls

Place 6 dough strips side by side, and using your fingers, unite the tops. Braid 

Place challah in a cookie tin lined with parchment paper and let the dough rest for 90 minutes 

Preheat oven to 350 degrees Fahrenheit

Brush the top of the challah with the beaten egg.

Bake for 35-40 minutes or until the top of has browned 

Enjoy!