Chop 86 grams (3 oz) chocolate into fairly small pieces. Place in airtight container in the freezer. You'll stir these in at the end.
Chop 14 grams (0.5 oz) chocolate into small pieces. Place in a medium mixing bowl with a wire mesh strainer over it and set aside.
Scald. Combine milk, heavy cream, sifted cocoa powder, and rosemary in a small pot over low-medium heat. Stir frequently. When bubbles form around the edges of the cream, tilt the pot forward. If there are lots of active bubbles on the bottom of the pot, reduce heat to low or turn heat off and let steep for 10 minutes. DO NOT BOIL. A skin might form on the surface of the cream, that's okay. Just give it a stir every now and then.(If you don't see lots of bubble activity when you tilt the pot, return to heat and keep stirring and tilting until you see the bubbles.)
Ribbon. While the rosemary and cocoa steep in the cream, whisk eggs and sugar together in a large heat-safe bowl until pale and slightly frothy, about 1-2 minutes. If you pick the whisk up out of the bowl a ribbon of the egg mixture should trail from the end.
Temper. Place a folded towel under the egg bowl to stabilize it. Remove the rosemary from the cream and discard. Slowly pour the hot cream into the egg mixture, whisking constantly to prevent the eggs from scrambling. Once all of the cream has been whisked into the eggs, transfer the mixture back to the pot and return to low heat.
Cook. Cook the mixture over low-medium heat, stirring constantly with a wooden spoon until it coats the back of the spoon (if you draw a line through the mixture on the spoon, the line should stay visible with clean edges; you may also notice the bubbles on the surface disappear).
Strain. Strain the hot ice cream base into the bowl you set aside earlier; pour it through the wire mesh strainer over the chopped chocolate. Let sit for 30 seconds to melt the chocolate, then stir until combined and no streaks of chocolate remain.
Chill. Transfer the ice cream base to an airtight container in the fridge and let chill for 3 hours or overnight.
Churn. Churn according to your ice cream maker's instructions. Stir in frozen chocolate chunks while the ice cream is still soft (or add them to the ice cream maker when it's almost done), then transfer the ice cream to an airtight container in the freezer and chill for at least 2 hours before scooping.