Place the mascarpone cheese in a large bowl and stir with a rubber spatula. Place a fine mesh strainer over the bowl. The finished custard will be poured through the strainer.
In a 4 quart non-reactive heavy saucepan combine the milk, the heavy cream and 1/2 cup of the sugar. Warm the milk cream mixture over medium low heat until small bubbles from at the edges of the pan.
In a medium bowl combine the egg yolks, 1/4 cup sugar and salt and whisk together into the egg yolks are lighter in color. Slowly pour half the warm milk mixture into the egg-sugar mixture whisking constantly to temper the eggs.
Return the mixture to the saucepan and cook over medium low heat stirring constantly with a heat resistant spatula or wooden spoon until the custard reaches 180 degrees F and slightly thickened. Do not let the custard boil or will have a grainy texture.
Strain the custard into the bowl with the mascarpone cheese. Whisk until the mixture in smooth. Add the vanilla extract and the lemon juice. Cover the bowl with plastic wrap and refrigerate the custard for at least 4 hours or until completely chilled.
This recipe make 4 1/2 cups of custard.
For the Roasted Sour Cherries
Preheat the oven to 375 degrees F.
To get 4 cups of pitted sour cherries you will need about 2 pounds of cherries. For roasting the cherries, you will need a ceramic dish that is about 3 quarts so the cherries lay in a single layer.
Combine the cherries, 1/2 cup sugar and salt in a bowl and stir to combine. Place the cherries in ceramic dish in a single layer.
Roast the cherries for 15 minutes, then stir with a large metal spoon and taste for the level of sweetness. If you want the cherries sweeter, add 1/4 cup of sugar, stir and return to the oven. Roast for another 10 minutes, test again for sweetness and add the remaining 1/4 of sugar if you prefer. Roast the cherries for another 10-15 minutes just until the cherries start to shrivel and are darker in color.
Scrape the cherries into a metal bowl and cool to room temperature. Place about 2/3 of the cherries in a blender and puree until smooth. Strain the puree through a fine-mesh strainer to remove the skins. Combine with the whole cherries and set aside. You should have about 1 1/4 cups of pureed and whole cherries.
For the Mascarpone Sour Cherry Ice Cream
Churn the custard in an ice cream machine according to the manufacturer’s instructions. Scoop the soft ice cream into a large bowl and swirl in all but 1/4 cup of the cherry puree. Place the ice cream into freezable container and freeze for about 4 hours.
If the ice cream machine has an open top add the cherry puree in large spoonfuls to the ice cream in the machine during the last couple of minutes of churning. This method will also create a nice swirl.
Serve and top with some of the remaining cherry puree.