Prepare an ice bath by placing a shallow baking dish nestled inside a roasting pan filled with ice and a little cold water. The ice and water should not go more than halfway up the pan. Add ice as it melts, but do not let the water rise to the level of the top of the baking dish.
In a small bowl, whisk together the sugar, milk powder, tara gum (if using) and glucose powder. In a tall cylindrical 1.5 litre (1½-quart) mixing vessel, blend the milk, condensed milk and egg yolks with a hand blender. Add the dry ingredients and blend again to dissolve all the solids.
Pour the mixture into a medium saucepan. Scrape the vanilla seeds into the mixture and add the pod. Cook over medium-low heat, whisking constantly, until it reaches 165°F (75°C) on an instant-read thermometer.
Once the base reaches 165°F (75°C), immediately remove it from the heat, fish out the vanilla pod and pour the mixture back into the tall mixing vessel. Add the heavy cream and ghee and blend with a hand blender for 2 minutes to fully homogenize.
Pour the base through a fine-mesh sieve into the prepared ice bath to cool. Whisk in the kala namak (if using), adding a little more at a time until the desired flavour is achieved. Remember that the final flavour of the ice cream will be muted once frozen.
Once completely cool, transfer to an airtight container and refrigerate for at least 12 hours and up to 3 days.
When ready to begin, line two metal loaf pans with wax or parchment paper. (Alternatively, you can use silicone loaf pans.) Place the loaf pans in the freezer to chill. Quickly blend the ice cream base once more with a hand blender or whisk before pouring it into an ice cream machine. Churn the ice cream until it reaches the texture of very stiff soft-serve and the surface looks dry, about 25°F (–5°C) or colder on a thermometer gun.
Divide the ice cream evenly between the chilled loaf pans. Press a piece of wax paper directly on top of the ice creams and place them in the freezer while preparing the crust.