Lightly oil a large bowl and set aside until needed.
Line a 23cm cake tin with baking paper and set aside until needed.
Place the yeast, 2 teaspoons of the sugar and all of the milk into a small bowl and let it sit for 5 minutes. After this time the mixture should have started to foam which is a sign the yeast is active.
In a large bowl, add the flour, cinnamon, egg, butter, chocolate chips, remaining sugar and activated yeast mixture. Use a butter knife to mix and combine the ingredients until a dough forms - don't worry, it will be sticky and the chocolate chips will have melted a little through the dough.
Turn the dough onto a floured bench and knead for approximately 8 minutes or until the dough begins to feel elastic.
Place the dough into the prepared oiled bowl, cover with a tea towel and sit in a warm place for around an hour or until the dough has doubled in size.
Chop the Mars Bars into 12 even pieces and remove the dough from the bowl. Divide the dough into 12 even pieces and place a piece of Mars Bar into the centre before rolling into balls.
Place the dough balls into the prepared cake tin, cover with a tea towel and place the tin in a warm spot for another 30 minutes to allow the dough to again rise.
While the dough is rising, preheat your oven to 200 degrees.
Once the buns have again risen, place the tray into the oven to bake for 20 minutes, or until the buns spring back when touched.
To prepare your glaze, place the apricot jam and water into a small bowl and heat in the microwave for 30 seconds before mixing to combine.
Brush the glaze over the still hot Hot Cross Buns before carefully transferring the buns to a wire rack to cool.
When the Hot Cross Buns have completely cooled, melt the extra milk chocolate and place it into a piping bag to pipe the crosses onto the buns.