Peel and cut the mango into pieces. Squeeze as much flesh off as possible. Blend it in the blender or food processor along with the lemon juice. Strain the mango mix into a bowl, so that the stringy bits are eliminated from the puree. You should have about 1 1/4 cups mango puree.
Whisk egg yolks and sugar till pale and lemony.
In a medium/heavy saucepan, bring milk and cream to a simmer. Turn off heat and whisk half of the mixture into the yolks.
Return everything to the sauce pan over a very low heat and keep on stirring it till it thickens.
Remove from heat and strain it into a large bowl. Let it cool for 5 or 6 minutes and then mix in mango puree.
10 mins before processing in the ice cream machine, put the mango custard into the freezer and also put the ice cream dasher into the freezer. (this SHOCKS the mix so that not much air is whipped in).