Cherry Sauce : Place all ingredients in a small saucepan and simmer on medium heat, stirring occasionally, until sauce has reduced and is somewhat sticky (about 15 minutes).
Towards the end of simmering, add a splash of cherry liqueur to taste, if using. Reduce heat to very low to keep warm.
Lava Cakes : Generously grease four round ramekins (8-10cm diameter) with butter and dust with cocoa powder. Invert to remove any excess cocoa.
Place butter and chocolate in a microwave-safe jug and microwave on medium-low in 30 second bursts, stirring in between, until melted and smooth.
Using an electric mixer, beat eggs, yolks, sugar and salt together until pale and thick (about 5 minutes).
Add melted chocolate mixture and cherries to egg mixture. Sift flour over the top. Gently fold in until well combined.
Divide evenly between prepared ramekins. Bake for 13-15 minutes (sides of the cakes should be firm but the centres still soft).
Allow to cool for 1 minute, then carefully invert onto individual serving dishes. Top with a scoop of vanilla ice cream or thickened cream. Drizzle cherry sauce around the sides and over the top. Decorate with chocolate curls, if desired. Serve immediately.
Additional tips
Fresh or tinned cherries can be used in this recipe.