10 sprigs lemon verbena (substitute other herbs like thyme, mint or rosemary)
1/2 cup water
3 tablespoons pectin powder or tapioca starch
1/4 cup freshly squeezed lemon juice (more if desired)
Sterilize lids and jars for 10 minutes in a large pot of boiling water. They can stay in the hot water after sterilization until you're ready to use them. Put a few small, clean plates in the freezer to chill.
Bring a large pot of water to boil. While it heats, fill a large bowl with ice water and use a paring knife to lightly score the bottom of each piece of fruit with a small "X." Blanch the fruit in the boiling water until the skin starts to peel back, about 1 to 2 minutes. Using a slotted spoon or tongs, transfer the fruit to the ice water. Once cool enough to handle, remove the skins from the fruit, cut them in half, remove the pits and thinly slice.
Put the sliced fruit in a medium bowl and, using a potato masher or wooden spoon, lightly smash the fruit into a chunky pulp. Stir in 1 cup of sugar and set fruit aside to macerate until the sugar has dissolved, about 5 minutes.
In a large pot, combine fruit mixture, lemon verbena and water. Place the pot on the stove over medium-high heat, stirring frequently with a silicone spatula, until it begins to boil. Once boiling, reduce the heat to medium and simmer, stirring frequently and lightly pressing on the fruit to break it up. Continue to cook until the mixture has thickened to the point where you can push a spatula through it and the jam does not immediately rush in to fill the space you've cleared (about 10 to 12 minutes). Remove the lemon verbena sprigs and reserve for another use.
In a separate bowl, combine the pectin powder (or tapioca starch) with the remaining sugar. Add this to the fruit mixture and simmer until thick and glossy, 12-15 minutes. Remove the jam from the heat. Stir in the lemon juice, taste and add more if you'd like.
Using a clean spoon, drop a bit of jam onto one of the chilled plates and angle the plate down a bit to see if the jam runs. If it runs quickly, the jam hasn't been cooked long enough yet. Put jam back on the heat and try this test again in a few minutes. If the jam moves on the plate only a small amount, it's ready.
Set a large stockpot filled with enough water to just cover the jars on high heat. While waiting for it to boil, skim off any foam that's settled on the top of the jam. Ladle the hot jam into the jars, leaving 1/4-inch headspace. Remove any air bubbles and adjust the headspace, if necessary. Wipe the rims with a clean cloth and seal with the lids.
Process the jars for 10 minutes in a boiling-water bath. Using tongs or a jar lifter, remove from the water and set on a towel to cool and seal. To test the seal, run your finger over the lid after 30 minutes. You should feel a slight depression in the center of the lid. The sealed jars can be stored in a cool, dark place for up to one year. If a jar fails to seal, put it in the refrigerator and use within one month.