5 tbsp vodka (optional for Mrs Jackson after having us for a week) [Joking]
Place 1/4 cup of milk and the tapioca starch in a small bowl and whisk to combine. Set aside.
Reserve one sprig of lemon balm to tuck into the ice cream base once it is cooked. Set aside.
Combine the heavy cream, remaining lemon balm, remaining milk, and the sugar in a small saucepan over med heat. Stir frequently until the sugar is dissolved and the mixture just begins to steam.
Remove from heat and let the mixture steep for 30 minutes.
After 30 minutes, remove the lemon balm and place the mixture over medium heat again.
Stir frequently and bring to a steady simmer.
Once the mixture simmers, give the reserved milk/tapioca starch slurry a final stir and whisk it into the ice cream base, stirring constantly. It should thicken quite quickly. The base is done when it coats the back of a spatula.
Remove from heat and stir in vanilla extract and vodka, if using. The vodka improves the texture of homemade ice cream and you can’t taste it.
Place the reserved sprig of lemon balm in a heatproof bowl and pour the warm ice cream base over it.
Cover and refrigerate until completely cool and process in an ice cream maker according to the manufacturer’s instructions.