Soak the dates in just enough water to almost cover them. Water level should not cover the top of dates. Soak in a way that the top layer of dates is half submerged in water. Soaking time will be less in hot weather and more in winters and will also depend on how fresh and soft the dates are. It can range between 4-8 hours. You can check after 3-4 hours if the dates have become soft and the seeds are sliding off very easily without applying any pressure.
Now remove all seeds. Be careful, you don't want to accidentally put any seeds in your blender and ruin the blades.
Add all dates in the blender along with the soaking water.
Blend until nice and smooth.
Dates puree is ready. You can use it immediately or keep it in the refrigerator for 3-5 days. If you wish to keep it longer, then freeze it in any airtight container.