Put the martini glass in the freezer for at least 5-10 minutes.
Fill the cocktail shaker halfway with crushed ice.
Add the liqueur and half-and-half.
Shake vigorously for 5-10 seconds. This step is the most important.
Using the cocktail strainer, strain into a chilled glass and add your favorite toppings. I added a little bit of cinnamon and cocoa powder and whole coffee beans.
Notes
This recipe yields only one martini, but feel free to double the recipe and add all ingredients to the same cocktail shaker. There will be plenty of space.