Skyr
Breakfast, Dairy, Desserts, Snacks And Appetizers, Vegetarian
Ingredients
Dutch Oven
1 Gallon Whole, 2%, or Skim Milk
1/2 of a rennet tablet (*1)
Water
Thermometer
1 container plain, vanilla, or coconut Icelandic skyr with live active cultures (4-5 oz.) or saved 1/2 cup from a previous batch
Yogurt bag(s) with a draw string
Container with lid for incubating the Skyr (if needed)
Container with lid for storing the Skyr
Yogurt maker, instant pot, or dehydrator
Large bowl (for holding the yogurt bags while filling)
Spatula
Ladles
Small bowls
Spoons
Description
Skyr is an Icelandic yogurt with a tart flavor and thick texture bordering on cream cheese-like. It can be hard to find authentic skyr, as well as pretty expensive outside of Iceland.
With your initial investment in supplies, this may not seem cheaper, but it is in the long run when you are only buying the milk.
Directions
Clean everything you will use with soap and hot water before using it; you don't want the wrong kind of bacteria to accidentally get into the yogurt.
Pour the milk into the dutch oven and add the thermometer. Heat the milk slowly to between 185 and 190F (I usually aim for 187F). Stir frequently with a spatula. 
Milk has a tendency to scorch to the bottom of the pan, so don't scrape too hard if you notice this has happened; you don't want this in your finished skyr.
Once it has reached the correct temperature, turn off the heat and let it cool back down to 110F. Move it, and the thermometer, to what you will be incubating it in while it cools.
Put the partial rennet tablet in a small bowl and add a small amount of water, just enough to cover the tablet.
Remove the thermometer. Stir spoonfuls of the warm milk into the saved or storebought Skyr, until it is watery, then stir into the pot of milk. Mix until completely incorporated.
Stir the rennet tablet with a spoon to make sure it is completely dissolved, then stir it into the milk. If using a container, put on the lid.
Now it is ready to incubate. Follow the instructions for what you are using and set the temperature where you can, between 95-110F. 
Incubate 12-18 hours. (How long I leave it often depends on what time it will be when it's ready.)
The Yogurt should be thick with whey floating on top or thick with whey throughout.
Don't worry if it seems very soupy instead. As long as there are lots of solids in the mix you will get yogurt, it will just be thinner than is typical for skyr. Rennet can vary and it may be that you need more next time. (*1)
Ladle whey off the top until you can see the solids if necessary.
Put your yogurt bag(s) in a large bowl and fold over the top(s). Use a ladle to move the skyr to the bag(s).
Close the bag(s). Suspend over a sink or the bowl.
Let drain until it stops dripping whey, checking periodically. Expect it to take several hours.
If desired, save the whey for other uses like Whey Rolls And Breadsticks.
Flip the bags inside out over a bowl or the container you will be storing the yogurt in and use a spatula to get it all out. Set aside 1/2 cup to make another batch later.
Optional: Stir in 1/4 cup of honey to sweeten.
Refrigerate for at least 6 hours before eating and eat within 14 days.
Making more:
Make another batch from the saved portion within 7 days, or freeze and use within 4 weeks. A yogurt culture frozen longer will lose potency and you will need to start over with another store bought container.
Pull the frozen yogurt out to defrost while you get everything else ready. It will be curdled and separated as it thaws, but will still work fine.
Notes
*1 1/4 of a tablet is generally the recommended amount, so you may want to start with that. For me (plant based) Junket actually needed 1/2 tablet (.4 grams) to get the texture result I wanted, so I changed it.
Washing the yogurt bag(s): Put the bags, inside out, in a sink full of cool soapy water and let soak for a bit. Rub the mesh to get all of the residue off. Drain the sink and rinse the bag(s) thoroughly with warm water. Let dry sitting upright, then flip right side out and put away.