Wash and hull the fresh strawberries first. Slice the large berries into small halves. Keep the tiny berries whole for texture. Place them in your large heavy pot.

Pour the white sugar over the berries. Stir them gently with a wooden spoon. Let them sit for thirty minutes total. This helps the berries release their juice.

Grate the green apple into the pot. The apple has natural pectin for thickening. Add the fresh lemon juice and zest. This keeps the color very bright red.

Place the pot on the stove burner. Turn the heat to a medium setting. Stir until all the sugar is dissolved. The mixture will start to look liquid.

Bring the mixture to a full boil. Stir it often so it does not burn. Watch the bubbles get thick and slow. This process takes about fifteen minutes total.

Place a spoonful on a cold plate. Push it gently with your clean finger. If it wrinkles, the jam is ready. If it runs, boil for more time.

Remove the pot from the hot stove. Stir in the vanilla and the salt. Remove the strip of lemon zest carefully. The jam will smell very sweet now.

Place the funnel over a clean jar. Ladle the hot jam into each jar. Leave a small space at the top. This is called "headspace" for the seal.

Wipe the rims of the jars clean. Put the lids on very tightly now. Let them cool on the kitchen counter. Put them in the fridge once cold.