Place chopped mamey in a food processor or blender, and puree until completely smooth. Add the puree to a bowl along with ½ cup of the heavy cream.
Heat the remaining ½ cup heavy cream, milk, brown sugar and salt in a small saucepan over medium heat. In a separate medium bowl, whisk the egg yolks. Once the cream mixture has tiny bubbles around the edges, slowly pour it into the egg yolks, whisking all the while. Once combined, add back to the saucepan and stir constantly over medium-low heat until the mixture thickens and coats the back of a spoon.
Pour through a fine mesh sieve into the bowl with the puree and heavy cream. Whisk to combine and set over an ice bath to cool. Refrigerate until the mixture is thoroughly chilled. Freeze in your ice cream maker according to the manufacturer’s instructions.
Make about 1 quart