Destem sour cherries. Get rid of damaged ones or the ones with worms. Wash the remaining, destemmed cherries. (Optional: make sour cherry stem tea by drying the stems on a table for a few days.)
Layer sour cherries and sugar in the jar. Start with sour cherries, then generously cover with about 4 tablespoon of sugar. Repeat until you fill the entire jar.
Pour brandy in the filled jar slowly. Pour as much brandy as the jar can take. This process may take a few minutes. (My jar took about 1.5 cups after sugar and sour cherries. Yours may take more.) If space allows, add more sugar on top, and fasten the lid.
Take the jar outside, and leave in direct sunlight (or a place with a lot of light) for about 40 days or 6 weeks.
Every 4-5 days take a spatula with a long handle and mix the sugar and sour cherries well. Undo the lid, take out a few cherries from the top and mix thoroughly. Return sour cherries to the jar and fasten the lid.
After 40 days, strain the brandy into glass bottles. Keep remaining sour cherries to use in a dessert.
Serve sour cherry brandy (višnjevača) with dessert, with coffee, or as an aperitif.