In a large mixing bowl, thoroughly whisk together the all-purpose flour, granulated sugar, baking powder, and salt, ensuring there are no lumps.
In a separate bowl, combine the warm milk, melted butter, and egg. Whisk until well blended. Gradually add this wet mixture to the dry ingredients, stirring gently until just combined; the dough should be slightly sticky but manageable.
Turn the dough onto a floured surface, and knead gently for about 3-4 minutes until the dough becomes smooth and elastic. Cover the dough with a clean kitchen towel and let it rest in a warm place for 10-15 minutes to relax.
In a small mixing bowl, blend the ground cinnamon, packed brown sugar, cocoa powder, and vanilla extract to create a flavorful filling mixture.
Carefully roll out the rested dough into a rectangle shape, measuring approximately 12x18 inches. Using a brush or the back of a spoon, spread the melted butter evenly over the entire surface of the dough. Next, generously sprinkle the cinnamon mixture and evenly distribute the chocolate chips across the dough.
Starting from one long edge, tightly roll the dough into a log, taking care to keep it uniform. Pinch the seam to seal the roll securely.
Using a sharp knife, slice the log into 12 equal pieces. Arrange these cinnamon rolls in a greased 9x13-inch baking dish, leaving a little space between each roll for expansion.
Cover the baking dish with a towel, and let the rolls rise in a warm environment for about 30 minutes, or until they have doubled in size.
Preheat your oven to 350°F (175°C). Bake the rolls in the preheated oven for 20-25 minutes, or until they are beautifully golden brown on top.
While the rolls are baking, prepare the glaze by whisking together the powdered sugar, milk, and vanilla extract in a small bowl until the mixture is smooth and free of lumps.
Once the rolls are out of the oven, allow them to cool for a few minutes before generously drizzling the glaze over the warm rolls, letting it cascade into the crevices.