Soak the oats in cold water for at least half an hour, then drain and rinse them well. Place them in the jar of a blender, and blend for 30 seconds. Pour the oats into a nut bag and strain. Measure out 1 1/2 cups of the milk, then stir in the maple syrup, salt, and vanilla extract. Place a layer of blackberries in the bottom of your popsicle molds (you may have to cut larger ones in half), then sprinkle in about a half tablespoon of granola. Repeat the layers until all of the molds are nearly full. Pour the oat milk mixture over the top until they’re  full, then insert a stick into each one. Place in the freezer for at least 8 hours, or until frozen through. Then, remove them from the molds and enjoy immediately.