Cut the butter into small cubes and add it to a food processor together with the flour.

Pulse until a crumbly dough starts to form.

Add the egg (both yolk and white) and mix.

You may need a little cold water, so add it gradually, one tablespoon at a time, until the tart dough reaches the right consistency.

Take the dough out, form it into a ball, wrap it in plastic foil, and refrigerate for 1 hour.

After 1 hour, take out the dough and roll it into a tart pan (I used a 20 cm one). If you can't find a rolling pin, grease the pan with a little oil, wet your hands, and press the dough directly into the pan using the flat bottom of a glass. There's always a solution if you don't have the right utensils, space, or if you're feeling lazy like me! :)

Place the tart pan in the fridge.

Add the sour cherries to a pan, cover with a lid, and set the heat to high. The cherries will start to release their juice.

Add the coconut sugar and rum and lower the heat to medium. After 5 minutes, add the corn starch and mix.

Cook for 5 more minutes without the lid.

Spread the sour cherry mixture over the tart dough.

Bake at 180°C (350°F) for about 20 minutes, or until the dough turns golden.