Place the chocolate and most of the cream in a bowl or mug and melt. Stir to combine thoroughly. Save about 2 tbsp of cream for the top layer at the end.
Make the espresso.
Add the vanilla and sugar, if using, stir, then add the espresso.
Pour into the serving latte glass or cappuccino cup.
Froth the milk. Add to the coffee and stir gently.
Very gently, add the rest of the cream to achieve that layered look.
Notes
I always melt chocolate in the microwave and have never had a problem. I suppose the key is to adjust the power, especially with white chocolate as it burns easily. Mine is 1000 watts and I use it at 50% power to melt chocolate.