Whisk the egg yolks in a bowl until creamy and smooth. Set aside.
In a medium size saucepan, whisk milk, sugar, milk powder, and salt. Cook over medium heat, stirring frequently, until the mixture starts to simmer.
Gradually pour some hot milk mixture into the bowl with egg yolks, whisking as you pour. Stir to combine, then transfer the entire mixture back into the saucepan.
Place the saucepan back on the stove. Cook the custard over medium-low heat for a 2~3 minutes, stirring constantly, or until it thickens a bit and starts to coat the back of a wooden spoon.
Remove the pan from heat and stir in the heavy cream.
Stir in the mango mixture along with ground cardamom (if using) into the custard. Mix well, cover and refrigerate until thoroughly chilled, about 4-6 hours or overnight preferred.
Follow your ice cream maker instructions and churn the gelato until thick, at the very end of the churning, add the liqueur and churn until well mixed.
Transfer into an airtight freezer safe container.