Weigh out and combine the water-based ingredients (the witch hazel, aloe juice, lavender hydrosol, and cucumber extract) in a heat-safe container or double boiler insert.
In a separate heat-safe container (or double boiler insert), weigh out the oil-based ingredients (emulsifier, aloe oil, and cocoa butter).
Heat both containers over hot water until the emulsifying wax and cocoa butter melt. Ideally, the temperature of both should be around 75°C/165°F.
Remove the containers from the heat source and add the water-based ingredients to the oil-based ones. Blend with an immersion blender or a mini blender. (A milk frother also works.)
While the mixture is still warm, it will likely separate again. To make a stable emulsion, blend it every few minutes while it cools. It will start to thicken and stay together as it gets cooler.
When the mixture cools to a temperature of around 45°C/110°F, add in the cool-down phase ingredients (the vitamins, essential oil, and preservative). Continue to blend occasionally until the mixture reaches room temperature.
To sanitize the containers, spritz with alcohol and allow them to dry to help sanitize them.Using a broad-spectrum preservative, this should keep for around 3 months. (While it should keep longer than that, it's best to make small batches with homemade products that won't be tested for microbes.)The water-based ingredients can be substituted with distilled water. The oil or cocoa butter can be substituted with a different carrier oil of your choice. The cucumber extract can be subbed with glycerin (or distilled water).To adjust the viscosity (thickness) of the lotion, adjust the amount of emulsifying wax used. (Use more for a thicker lotion.) Check the dosing recommendations for your particular emulsifying wax.