Crumble or chop the crullers into small pieces. Do not over chop into crumbs, but make a variety of piece sizes. Set the doughnut pieces aside.

Gently heat the milk in a saucepan over low heat until hot but not boiling, and stir in the instant coffee granules until dissolved. Remove the milk mixture from the heat, and allow to cool.

Place the eggs in a mixing bowl, and beat for 3 minutes with an electric mixer until light, adding sugar about 2 tablespoons at a time until the sugar has been incorporated. Beat for 1 more minute, then beat the milk mixture and heavy cream into the eggs on low speed, until the mixture is smooth and creamy.

Place the mixture into an ice cream maker, and freeze according to manufacturer's instructions. When the ice cream is firm but not hard, lightly mix in the doughnut pieces. Pack the ice cream into a covered airtight container, and freeze for 6 to 8 hours, to ripen the flavor and firm the ice cream. Let the ice cream stand at room temperature for about 10 minutes before scooping into servings.