Stir about half the flour together with the salt in a large bowl.
Make a well in the center, and pour in the milk, cream, melted butter, and sugar.
Sprinkle the yeast on top of the liquids and allow it to dissolve (approx. 5 minutes).
Stir together until combined, then add the eggs.
Stir until fully incorporated, then add the remaining flour, a little at a time, until the dough is no longer sticky. (It should gather itself into a ball and pully cleanly away from the sides of the bowl. You may need slightly more or less flour.)
Cover lightly with plastic wrap and allow the dough to rise in a warm place until doubled in volume (approx. 1 hour).
Punch the dough down and roll it out to a thin, wide rectangle.
Spread the filling on top, leaving a bare margin around the edges for sealing.
Starting at one of the short sides of the rectangle, roll into a short, tight log.
Starting near the top of the log, slice the log in half lengthwise.
Twist the two long halves around one another and place in a loaf pan.
Cover lightly and set in a warm place to rise a second time until doubled (approx. 1 hour).
Preheat the oven to 350 degrees F and bake the bread until it registers an internal temperature of around 195 degrees F (approx. 1 hour).*
To Make the Filling
Chop the chocolate and place it in a heat-safe bowl.
Heat the cream (either in the microwave or in a pot on the stove over medium-low heat) until steamy.
Pour the hot cream over the chopped chocolate and allow it to stand for 5 minutes.
Stir the cream and chocolate together until smooth and combined.
Notes
*Tent with foil if the babka is getting too brown on top.