Preparation:
1. In heavy saucepan over low heat, bring milk and cream to boil. In medium bowl whisk eggs until frothy. Gradually sir in half of the hot milk mixture into eggs. Return milk and egg mixture to saucepan; whisk in sugar. Cook, stirring constantly, until mixture thickens and comes almost to a boil. Remove custard from heat; stir in white chocolate and vanilla.
2. Puree 1 avocado with about one-quarter of the custard until very smooth. Whisk avocado mixture into remaining custard until blended; cool to room temperature. Chop remaining avocado; fold into custard. Freeze in ice cream freezer according to manufacturer’s directions.
3. On rimmed baking pan, scoop ice cream into 12 mounds. Cover; freeze until firm, 2 to 3 hours.
4. In food processor, process cookies with nuts to form fine crumbs; transfer to medium bowl. Working quickly, shape each ice cream mound into a ball; roll in crumbs to coat. Return to pan; cover and freeze until ready to serve.
5. To serve, cut each ice cream avocado in half. Serve with a few berries and a drizzle of fudge sauce. Garnish with diced avocado, if desired.