In a medium saucepan over medium heat, add milk, coffee beans, sugar and salt. Stir and bring the mixture to a simmer – do not boil.
Remove from the heat and transfer the milk mixture to a small bowl. Add finely ground coffee, Tia Maria and vanilla extract; stir well. Place wax paper on top making sure it touches the surface to prevent a skin from forming and let the mixture steep for 1 hour.
Later, remove wax paper and discard it. Pour mixture into a fine sieve over a large bowl; discard coffee beans. Add sweetened condensed milk and stir to blend. Taste the custard and add powdered sugar if it’s bitter – keep in mind that the whipped cream has some sweetness to it; set aside.
In the bowl of a stand mixer, add cold heavy cream and powdered sugar. With the whisk attachment on, process on high speed until stiff peaks form.
Scoop half the whipped cream into the milk mixture and fold until mixed. Add the custard mixture to the remaining whipped cream and fold again until well combined.
Pour the mixture into an ice cream tub, cover and transfer to the freezer until it hardens, about 8 hours.