Place the almonds in a large bowl and cover with about 2 inches of water. Cover and let soak at room temperature for at least 8 hours, or refrigerate overnight.
Drain the almonds and rinse well under cool running water.
Add the soaked almonds, 4 cups of fresh water, and salt to a high-powered blender. Blend on high for 1-2 minutes.
Pour the mixture through a fine-mesh strainer lined with a nut milk bag, or a strainer lined with cheesecloth, set over a large bowl.
Gather the bag or cheesecloth and squeeze firmly to extract as much liquid as possible.
Stir in the dates, maple syrup, or vanilla extract, if using, and blend again briefly.
Pour into an airtight container or bottle and refrigerate.