Cut the apricots into small chunks. Crack open a few pits (around 10) and place the kernels aside.
Add the apricots, kernels, and caster sugar into a large, heavy pot. Scrape out the vanilla seeds and add them to the pot; also, throw the empty vanilla beans in there. Bring to a boil, lower the heat, and simmer for about 25 minutes, stirring constantly.
Remove the jam from the stove, add the juice of one lemon, and stir well. Spoon hot apricot jam into hot sterilized jars, and cover immediately with sterilized lids. Let the jars cool slowly.