1. Pour all the ingredients (other than the Tonka bean) into a cocktail shaker.Fill a coupette glass with ice to chill and then fill the cocktail shaker as well.
2. Put the other half of the shaker on top and shake aggressively. You want the ice to smash up while chilling the liquid down to help create that frothy top. Try to use ice fresh from the freezer as melting ice will dilute the finished product.
3. Once shaken, tap the side of the shaker to break the vacuum seal. Empty the ice out of the coupette glass then place the strainer on top of the shaker and pour the contents through the sieve directly into the glass.
4. Finely grate the tonka bean over the top of the creamy froth to your liking and serve.