In a medium saucepan, combine 2 cups of pitted cherries with a splash of water. Cook over low heat for about 10 minutes, stirring occasionally, until the cherries are softened and release their juices. Then puree it until smooth and strain through a fine mesh sieve to remove skins.

While the cherry puree is cooling, juice half a lemon into a small bowl, about 2 tablespoons of fresh lemon juice.

In a heatproof mixing bowl, whisk together 2 whole eggs and 2 egg yolks with 3/4 cup of granulated sugar until light and fluffy.

In a medium saucepan, combine the cherry puree and lemon juice over medium heat, stirring continuously until it starts to bubble gently. Gradually add a spoonful to the egg mixture and whisk until combined.

Pour everything back into the saucepan and cook over low heat, stirring constantly for about 8-10 minutes until thickened enough to coat the back of a spoon.

Remove from heat and stir in 4 tablespoons of cold butter until melted and incorporated.

Cool to room temperature, then refrigerate for at least an hour before storing.