Combine the cream and fennel seeds in a small heavy saucepan, and bring just to a simmer. Remove from the heat, cover, and let steep for about 30 minutes.
Meanwhile, prepare an ice bath.
Then combine the milk, ½ cup sugar, and a pinch of salt in a medium heavy saucepan, and bring just to a simmer, stirring to dissolve the sugar.
In a large bowl, whisk together the egg yolks and the remaining ¼ cup sugar. Add the hot milk mixture in a slow stream, whisking constantly. Return the mixture to the medium saucepan and cook, stirring with a wooden spoon, until the mixture coats the back of the spoon and registers 175°F on an instant-read thermometer. (Do not allow it to boil.) Immediately strain through a fine-mesh sieve into a metal bowl. Cool in the ice bath, stirring occasionally.
When the custard is cool, strain the fennel cream through a fine-mesh sieve into the custard, pressing on the solids. Continue to chill in the ice bath until the custard is very cold. (Alternatively, cover the mixture, and chill it in the refrigerator overnight.) Freeze in an ice cream maker. Transfer to an airtight container, and put in the freezer to harden, about 1 hour.
Yield: 1 quart