If you'll be canning the jam, prepare the jars and hot water canner according to the instructions below.

In a wide pot, stir together strawberries, rhubarb, butter, cardamom, pepper, and calcium water.

Cook, stirring frequently, over medium heat until the fruit starts to release its juices.

Raise heat to high and bring to a full boil. Then reduce heat again and simmer, stirring frequently to prevent burning, until fruit has softened completely and largely broken down, about 15 minutes.

In a small bowl, whisk the sugar and pectin together thoroughly.

Add sugar mixture to pan and whisk constantly while mixture returns to a full boil. Simmer briskly for one to two minutes.

Remove from heat and stir in vanilla.

Funnel into jars, leaving ½-inch headspace. Refrigerate once cool or proceed to canning instructions.

To prepare the hot water canning bath, place your rack on the bottom of your canning pot and arrange the jars in the pot.

Fill the pot with water to cover the jars by about an inch.

Put the pot on the stove and bring the water up to a boil. While the water comes to a boil, make the jam.

When the jam is ready, lift the jars out of the canner with a jar lifter, carefully pouring out any water. You can turn off the heat for a bit while you fill the jars.

Funnel the jam into the jars as noted above.

Wipe the rims completely clean. Place lids atop jars and screw on rings completely but not too tightly. You're aiming for "fingertip tight," which means as tight as you would comfortably screw them on with your fingertips. This allows oxygen to escape while processing.

Use the jar lifter to place the filled, closed jars into the canner. Turn the heat to high and bring the water up to a full boil.

When the water reaches a boil, set a timer for 10 minutes. Keep an eye on the water. It should boil for the full 10 minutes, but you may want to lower the heat to avoid the kind of manic boil that would lead to splashing.

When the timer rings, turn off the heat. Carefully use the jar lifter to remove the jars from the water. Place the jars on silicone trivets or a kitchen towel (and not directly on the counter, where the sudden temperature change could crack the jars).

Let the jars cool until they're easy to handle. You may hear popping sounds as the jars seal, which is fun fun fun. Remove rings and test seals. The center of the lid should be depressed, and the lid should stay firmly in place when you invert the jar.

Make sure the sealed jars are clean, and store in a cool, dry place (without rings) for up to a year. Refrigerate any unsealed jars and use within three weeks.