Wrap grated ginger in cheesecloth and tie with string.
In medium heavy saucepan over low heat, cook cheesecloth-wrapped ginger, sugar, rhubarb, crystallized ginger and water, stirring constantly, 7 minutes or until fruit softens. Remove from heat; stir in cream. Return to medium-low heat and cook just until bubbles form around edge, stirring regularly. Remove from heat. Gradually whisk into yolks.
Return mixture to clean pan; add milk. Cook over low heat, stirring constantly, 12 minutes or until thick enough to coat back of wooden spoon. Do not boil. Remove from heat; stir in vanilla. Cover tightly; refrigerate 3 hours to overnight.
Remove and discard cheesecloth with ginger. Transfer mixture to ice cream maker. Process according to manufacturer's instructions. Transfer ice cream to airtight container, freeze at least 4 hours to overnight to achieve smooth, dense consistency.
Makes 3 cups.
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