Wash the sea buckthorn berries thoroughly and remove any stems or leaves.

Place the berries in a large pot with 2 cups water and bring to a boil. Stir frequently, mashing the berries to encourage them to fall apart and release their juices (about 5 to 10 minutes).

Remove from heat and strain the juice through a jelly bag or double layer of dampened cheesecloth (for jelly), or through a fine mesh strainer or food mill (for jam). Both will have seeds removed, but jelly will only use juice while jam uses juice and pulp.

Add the strained juice (or juice and pulp) back into a jam pot.

Add the powdered pectin, stirring to dissolve completely.

Turn on the heat and bring to a boil. Boil hard for 1 minute.

Add the sugar, stirring to incorporate. Return to a boil and boil hard for 1 more minute.

Turn off the heat and ladle into prepared jam jars, leaving 1/4 inch headspace.

Wipe the rims of the jars with a clean, damp cloth to remove any residue. Put the lids on and screw the bands tightly.

Place the filled jars in a boiling water canner. Make sure that the jars are fully submerged and process for 10 minutes (or 15 minutes if above 6,000 feet in elevation).

Remove the jars from the canner and let them cool on a towel or cooling rack.

Check the seals once cool and store the sealed jars in a cool, dark place. Refrigerate any jars that did not seal properly and consume them within a few weeks.