Proof the yeast by combining warm milk, a pinch of sugar, and the yeast. Let sit 8 minutes until foamy.
Mix the dough by combining flour, sugar, and salt, then adding eggs, vanilla, and the yeast mixture. Stir until a shaggy dough forms.
Knead for 8 minutes, then add softened butter in pieces and knead 5 more minutes until smooth and slightly tacky.
First rise: Cover and let the dough rise in a warm spot for 1.5 to 2 hours until doubled.
Make the filling by melting chocolate chips and butter together, then stirring in cocoa powder, powdered sugar, and espresso powder. Cool until spreadable.
Roll the dough into a 12x16 inch rectangle on a lightly floured surface.
Spread the filling evenly over the dough, leaving a small border at the edges.
Roll and cut: Roll the dough tightly from the long side into a log, then cut in half lengthwise.
Twist the two strands around each other with cut sides facing up, then place in a greased 9x5 inch loaf pan.
Second rise: Cover and let rise 45 minutes to 1 hour.
Bake at 350°F (175°C) for 35 to 40 minutes until deep golden brown. Cool at least 20 minutes before slicing.