Peel and grate the apples into a bowl. Tip: grate each apple on one side down to the core, then turn the apple and continue grating until all you have left is the core.
Add the brown sugar, the lemon juice, and the spices. Feel free to play with the proportions of these spices. In fact, you may want to make your shrub using apple pie spices. Try 1 tsp. Cinnamon, 1/2 tsp. Nutmeg, and 1/4 tsp. Cloves.
Stir the mixture for a few minutes until it is well-blended, then cover tightly and set aside for 2-5 hours.
After a few hours, stir it again, then cover it and set it aside on your counter or in the fridge. Wait 2-3 days.
After 2-3 days, place a strainer over a medium size bowl and pour the mixture through it. Use a large spoon to press as much juice out of the apples as you can, then discard the fruit.
Measure the juice/sugar mixture (or eyeball it). Add apple cider vinegar in a 1:1 ratio. Add more vinegar if you like. (I added about 25% more vinegar.)
Optional: heat the mixture in a saucepan over medium high heat and simmer gently for 3-5 minutes to pasteurize it.
Pour your shrub into a clean jar or bottle and tightly cover. You can use it now, but recommended that you wait a few days to let the flavors marry and get happy.