Whisk together sugar and yolks until mixture is fluffy and almost white. Set aside.
In a medium pot, slowly bring cream and milk to a boil. Remove from heat, pour a little bit of milk into the sugar and yolk mixture and whisk immediately. Continue until all fully combined.
Transfer liquid back to pot and reduce heat to low. Cook for about 10 minutes, stirring frequently, until liquid thickens and coats the back of the spoon. Do not let it boil. Transfer custard to a bowl and chill for at least 3 hours.
Whisk mascarpone and vanilla into the custard. Transfer to ice cream maker and follow the maker’s directions on churning. Freeze in an air-tight container overnight before serving.
Top with raspberries, figs, grilled peaches, or whatever else strikes your decadent fancy.