Whisk the half-and-half and cocoa powder together in a saucepan and bring the mixture to a simmer over medium heat. Beat the egg yolks and Swerve together in a bowl until light and fluffy. Add the vanilla extract and a pinch of salt. Temper the two mixtures together by stirring ¼ cup of the chocolate mixture into the egg yolk mixture, and then slowly pour it all back into the chocolate mixture in the saucepan. Simmer over low heat, stirring constantly, until the mixture has thickened and coats the back of spoon. Take it off the heat just before it boils.
Chill the mixture for 3 hours or overnight. Once chilled, transfer the mixture to the ice cream maker and churn according to the manufacturer instructions. Serve the ice cream immediately or transfer to a container and store in your freezer.
If you choose to freeze the ice cream in containers, allow the ice cream to sit out on the counter for 20 to 30 minutes before serving for a scoopable, creamy consistency.