Prepare your pan with parchment paper to fit and completely line the pan for easy removal of the marshmallows when they're done. Also, get your candy thermometer ready*.
Place 1/2 cup of butterfly pea flower tea, 2 1/4 cups of organic cane sugar, and 1/2 tsp. of sea salt into a heavy bottomed pan over medium heat. Mix slowly and consistently until the sugar melts.
Heat the syrup to 238°F - 240°F (114°C - 116°) while slowly stirring the syrup to prevent scorching. Don't mix too vigorously or introduce air into the syrup. Use a candy thermometer to be sure of temperature. This usually takes 5-10 minutes.
Using hot mitts to hold the syrup pot, have a helper turn the stand mixer to low while you slowly (so slowly) drip the hot syrup down the inside of the mixing bowl. Be patient and continue to drip slowly.
Have your helper turn up the mixer one or two notches to speed up the mixing process as you continue to add more syrup. Hold the pot while your helper scrapes out the rest of the syrup into the bowl.
Add peppermint essential oil or extract, if you're using it.
Put the mixing collar on and turn the mixer up to high. You may need to use a kitchen towel to cover any openings in the collar to prevent splashing until the marshmallow begins to set up. Watch for the mix to bulk up, change color, and thicken.
Once you have soft peaks, stop the mixer, bang off the whisk attachment to remove excess marshmallow, and QUICKLY put all the marshmallow fluff into your pan.
Carefully bang the pan on the counter to level the marshmallow and smooth the top as much as you can. It will be quickly drying as you work, so just do your best.
Cover with a mesh screen or parchment paper (don't let it touch the marshmallow) to air dry. I usually add a kitchen towel on top to keep out bugs and children. The longer they sit, the dryer the marshmallows will be.