Fill the bottom portion of a double boiler with 2-3” of water. Make sure the water doesn’t touch the bottom of the double boiler insert! Place over a stove set to medium heat.
While the water heats up, add the macadamia butter, cacao butter, and vanilla paste into the double boiler insert. When the water starts to simmer, reduce the heat to medium-low. Whisk occasionally until completely melted. Turn the stove off.
In a small bowl, whisk together the erythritol, dried milk, and salt. Slowly whisk into the stovetop mixture.
Whisk in the stevia extract (it will thicken).
Spoon the mixture into chocolate bar molds. Refrigerate until firm. Store in a tightly sealed container in the fridge for up to 2 weeks.