Place the magnesium flakes in a small bowl and pour the boiling water over the top of them. Stir until the flakes are dissolved. Set aside.
Melt the coconut oil, beeswax, and cocoa butter in a double boiler. Remove from the heat and allow it to cool slightly.
Add the lavender essential oil and magnesium to the melted coconut oil, beeswax, and cocoa butter.
Whip the lotion using an immersion blender or a small hand mixer. Store in a glass mason jar with an airtight lid.