(Optional) Soak cherries overnight with kirsch / cherry liquor.

Brush 2 ramekins (170 ml capacity) with butter, then evenly coat with granulated white sugar. Tap out any excess sugar. Place ramekins on tray and set aside.

Using bain-marie / heated water bath, melt chocolate and butter then set aside. Bain-marie method means to put the heat-proof bowl of chocolate and butter over a pot of steaming water.

In a medium bowl, whisk together egg yolk, whole egg, sugar and salt until foamy and lightened in color.

Whisk melted chocolate into egg mixture. To prevent cooking the egg, keep whisking while pouring the hot chocolate. Mix just until combined.

Add all-purpose flour and fold using spatula just until combined.

Scoop batter into each ramekin a little under halfway. Then add cherries in the middle. Cover them with more batter, leaving about half inch from ramekin's top.

Smooth the top with offset spatula or the back of a spoon. Bake at 220°C / 425°F for 10 to 15 minutes. Note: to get that perfectly molten lava cake, do a test-bake and adjust baking time accordingly.

Let cool for 5 minutes on a cooling rack. Then carefully run a paring knife around the edges. Unmold the cake by turning it over on a plate. Best served when it is still hot.