Using a double boiler or a heatproof bowl over a pot of simmering water, melt 12 oz of beef tallow over low heat until fully melted.
Remove the melted tallow from the heat and add 4 oz of avocado oil. Stir to combine.
Place the bowl with the oil mixture in the freezer for about 30 minutes, or until the edges begin to solidify.
Remove the bowl from the freezer, add 1 tbsp of arrowroot powder, and use a stand mixer with a whisk attachment to whip the mixture until it reaches a creamy, almost whipped consistency.
If desired, add 20 drops of your favorite essential oil and mix until the fragrance is evenly distributed.
Transfer the whipped tallow lotion into two 8 oz glass jars. Label the jars and store at room temperature away from direct sunlight.
Allow lotion to sit for at least 24 hours to "set."