Wearing gloves, goggles & long sleeves, weigh the cooled peppermint tea into a heat-proof pitcher. Weigh the lye next, then carefully sprinkle and stir it into the water. Set the solution aside in a safe place to cool.
Let the lye solution cool for 30 to 40 minutes so that the temperature drops to around 100 to 110°F (38 to 43°C).
Measure out the oils by weight. Weigh and melt the coconut oil, then combine it with the other oils. This should bring the temperature of the oils up to somewhere around 90 to 100°F (32 to 38° C). If needed the oils can be warmed slightly to bring the temperature up to 90 to 100°F (32 to 38° C).
Pour the lye solution into the oils. Using a combination of hand stirring and a stick (or immersion) blender, mix until trace is reached.
Add the essential oils then pour the soap mixture directly into a mold, cover and insulate with a towel or blanket.
Let the soap stay in the mold for 1 to 2 days, then remove from the mold and slice into bars. Cure in the open air for 4 to 6 weeks before use.
Notes
To make the rosemary infused oil, infuse about one cup of olive oil with ¼ cup dried rosemary in a cool and dark place for at least 2 weeks (or use the quick heat method on the stovetop if you prefer). After the oil has infused and when you are ready to make the shampoo bars, strain out the rosemary through a fine mesh sieve.
When you are ready to make the shampoo bars, make the peppermint tea. To make the tea, steep one tablespoon of dried peppermint in one cup boiling water for 15-20 minutes. Let it cool to room temperature and strain before using.