Measure the oat milk in a glass measuring cup and heat in the microwave on high for 90 seconds or until it is hot but not boiling.
While the milk is heating, combine the cocoa powder, sugar, and salt in a 10-12 ounce mug. Pour the heated milk into the mug and whisk until the sugar is dissolved and the cocoa powder is fully incorporated. (A frother works well for this step). Stir in the vanilla extract.
Serve hot with your favorite toppings.
Stovetop
Pour the oat milk into a small saucepan and heat over medium low heat.
While the milk is heating, combine the cocoa powder, sugar, and salt in a small bowl. When the milk is hot but not boiling, whisk in the cocoa powder mixture until it is fully incorporated. Stir in the vanilla extract.
Serve hot with your favorite toppings.
Notes
If you're making several servings of hot chocolate at a time, keep warm in a kettle on the stovetop or in a slow cooker set on low.