In a large pot on the stove, add your pitted whole dates and 6 cups water. Set your burner to medium heat until it starts simmering, and then lower it to the lowest setting possible.
Simmer your dates and water, covered, for roughly 1 hour. At this point the dates should be getting super soft and the liquid should be golden brown in colour.
Take your pot off the stove and put it on a cooling rack. Let your cooked dates and water cool down to room temperature. This took roughly 2 hours for me. You can speed this up by putting it in the fridge.
Put your water and date mixture into a food processor or high-speed blender and blend for about 30 seconds or until the dates are in very small pieces. If you blend it for too long, it will turn into date paste and will be harder to strain. Alternatively instead of blending it up, you can use a potato masher to break down the dates.
Place your mesh strainer on top of a large bowl and put your nut milk bag inside of it. While holding your nut milk bag open, pour your blended date and water mixture completely into the nut milk bag. Once it's all in, start squeezing your nut milk bag until liquid starts coming out the sides and bottom. This will drain through your mesh strainer and into the large bowl. The mesh strainer will catch any chunks that may come out the top of the bag. Do this until you aren't able to squeeze any more remaining liquids out.
Remove the strainer and bag from the large bowl of liquid.
Rinse out your large pot so there are no remaining chunks of date and pour the liquid from your large bowl back into the pot.
Once again gently simmer on low heat for roughly 1 hour or until it starts reducing and getting thicker. Make sure to use the lowest setting so that it doesn't burn. Your date syrup will also thicken more once you have taken it off the burner.
Place your pot of date syrup back on a cooling rack and let it cool completely again. At this point you can pour it into a glass container or Mason jar and store it in the fridge.