Place sugar in an ovenproof shallow pan, and warm in a 250°F (120°C) oven for 15 minutes. Warming the sugar beforehand keeps the jam boiling evenly and ensures success.
Place berries in a blender or food processor until pureed. Strain the puree through a sieve pushing the puree through with the back of a wooden spoon to strain out all the seeds. Measure four cups of the puree, and place in a large saucepan, and bring to a full boil over high heat. Boil hard for 1 minute, stirring constantly. Add warm sugar, return to a boil, and boil until mixture forms a gel about 5 minutes.
To determine when the mixture gels, use the spoon test: Dip a cool metal spoon into the hot fruit. Immediately lift it out and away from the steam and turn it horizontally. At the beginning of the cooking process, the liquid will drip off in light, syrupy drops. Try again a minute or two later, and the drops will be heavier. The jam is done when the drops are very thick and two run together before falling off the spoon.
Make ice cream
In a medium bowl, beat the sugar and salt into the egg yolks until thickened and pale yellow. Set aside.
Bring the half and half to a simmer in a heavy medium saucepan or double boiler. Slowly beat the hot half and half mixture into the eggs and sugar. Pour the entire mixture back into the pan and place over very low heat or back in the double boiler. Stir continuously with a wooden spoon until the custard thickens slightly and coats the back of the wooden spoon. Be careful not to let the mixture boil or the eggs will scramble. Remove from heat and pour the hot custard through a strainer into a large, clean bowl. Allow to cool slightly, and stir in the cream and vanilla. Cover and refrigerate until cold or overnight.
Stir the chilled custard, and then freeze in your ice cream maker according to the manufacturer’s directions.
To make Baseball nut ice cream, wait until the machine has just finished freezing the vanilla ice cream. Remove the mixer bar before spooning the raspberry jam over the soft frozen ice cream. Lightly swirl the raspberry jam in a zigzag pattern with a small plastic or wooden spoon, and sprinkle in the cashews.
When finished, the ice cream will be soft, but ready to eat. For firmer ice cream, transfer to a freezer safe container and freeze at least 2 hours.