Make the rosemary-infused water in advance: fill a saucepan with 1 cup of water and ⅓ cup of dried (or fresh) rosemary. Heat it to no more than ~ 60 °C. Let it remain in heat for about one hour. Do not let it boil. Strain the rosemary leaves from the water.
Put a pan with water into the stove (tap water as this is for bagne-marie)
Measure the rosemary-infused water into one jug and let it heat in low heat (~ 60 °C)
Measure the oil phase ingredients into the double boiler.
Let the oils heat in low heat until the BTMS is fully melted
Measure the temperature of the water and oils. The temperature is not very important as long as the wax is completely melted and the water is hotter than the oils. Do not overheat your ingredients. They should all be around 50 °C - 60 °C.
Add the water to the oil mixture. The oils will turn from translucid to milky white
Mix it with the milk frother to emulsify completely the oils. You should get a white runny, creamy mixture.
Let the mixture cool down a bit, up until 45 °C - 50 °C, then add the cooling phase ingredients. Mix them well.
Remove a teaspoon of the mixture and measure the pH with a pH strip. It should be 5-6. Add a bit of lemon juice if it's too high, or add a bit of baking soda if it's too low. Mix well and measure the pH again.
Pour the mixture into your bottle, preferably a pump bottle. The mixture will thicken while it cools until it looks and feels like a lotion. Leave the bottle open while to cools down to release water vapours and prevent condensation inside the bottle.
Once completely cold, your hair conditioner is ready for use!