Carefully remove rind from oranges using a vegetable peeler, making sure not to get any of the white pithy part of the rind.
Combine orange rind and milk in a large saucepan, reserving orange pulp for another use. Bring milk mixture to a simmer over medium-high heat, stirring constantly.
Remove from heat; cover and let stand 20 minutes.
Strain milk mixture through a sieve into a bowl, discarding orange rind. Return milk to pan. Stir in chocolate. Bring to a simmer over medium-high heat, stirring constantly.
Pour into 6 mugs; top each serving with whipped topping.
