Melt the Chocolate: Melt the chocolate in a double boiler or in a microwave-safe bowl in short bursts, stirring in between, until smooth. Let it cool slightly.
Combine Ingredients: In a large bowl, whisk together the ricotta cheese, powdered sugar, and vanilla extract until smooth.
Fold in Chocolate: Gradually fold the melted chocolate into the ricotta mixture until fully incorporated. If using, gently fold in the whipped cream.
Chill and Serve: Pour the mousse into individual serving glasses or a bowl. Cover and refrigerate for at least 2 hours, or until set.
Serve: Garnish with chocolate shavings, fresh berries, or a sprig of mint.