My top tip: you also want to have *all* your ingredients handy, measured out, and make sure you won’t be disturbed for 15 minutes. Seriously! It's easy and quick, but you need to work through the steps continuously and quickly.
Add honey and water to a saucepan and heat up over medium heat, mixing gently until just incorporated (you want to ensure its mixed before it begins to heat up so it doesn't crystalize)(also if your raw honey was crystalized it'll take a minute to all come together). Continue to heat over low/medium heat, keeping an eye that it doesn't boil over and on the temperature (you want it to eventually reach 225ºF/107ºC).
Add egg whites and cream of tartar to your mixer with the whisk attachment and whip (over medium/high speed) until soft peaks form. Be sure to not over-whip, but your whites and honey should be ready at about the same time.
Once honey has reached 225ºF/107ºC, have your mixer running on medium and gradually pour the hot syrup in a slow and gradual pour (I wasn't so "gradual" once and the fluff survived, but try and temper your egg whites slowly). Continue whipping for 8 minutes on high speed, add vanilla extract and salt and whip for another 2 minutes.
Allow marshmallows fluff to come to room temperature and transfer to an airtight container.
And how long does it keep? Legend has it that homemade marshmallow fluff can keep for up to two weeks at room temp (stored in a cool, dry place). Tbch though I haven't yet had a whip last that long to test, but it will surely keep for a handful of days.