Remove the fruit residue from the mirabelle plum kernels, rub dry and pour into a bottle. Add 100 g sugar and top up with corn or vodka. Cap the bottle and shake.
The liqueur now has to go through 3 months. Shake the bottle every now and then. Then strain and pour into a clean bottle.
Caution: Do not use damaged cores. The kernels contain hydrogen cyanide (just like plum kernels), so do not crush the kernels and add them to the liqueur.
There's a recipe with plum kernels in the database here. Since this makes an excellent liqueur with an amaretto flavor, I tried Mirabelle kernels, which are also very tasty.