In a small saucepan, bring the maple syrup to a simmer and cook until reduced to 3/4 cup, about 5 minutes. Remove from the heat.
In a medium saucepan, combine the cream, milk, reduced maple syrup, and a pinch of salt. Bring to a gentle boil over medium heat. Remove from the heat.
Beat the egg yolks in a medium bowl. Whisk 1 cup of the hot cream into the egg yolks. Gradually add the egg mixture in a slow, steady stream, to the hot cream. Return to medium-low heat and cook, whisking, until the mixture is thick enough to coat the back of a spoon, about 5 minutes. Remove from the heat and strain through a fine mesh strainer into a clean container. Whisk in the maple extract. Cover with plastic wrap, pressing down against the surface to keep a skin from forming. Refrigerate until well chilled, at least 2 hours.
Remove from the refrigerator and pour into the bowl of an ice cream machine. Freeze according to the manufacturer's instructions. Transfer to an airtight container and freeze until ready to serve. Line a baking sheet with waxed paper and set aside. In a medium skillet, combine the butter and brown sugar. Cook, stirring, over medium heat until the sugar is dissolved. Add the nuts and a pinch of salt and cook, stirring, until toasted and evenly coated, about 6 minutes. Remove from the heat. Spread the coated nuts on the prepared baking sheet, stirring with a fork to keep from clumping.
When ready to serve, remove the ice cream from the freezer and let soften at room temperature for 10 minutes. Spread on a flat work surface and mix the candied walnuts, chocolate chips, and coconut into the ice cream. Scoop into cones and drizzle with nutty chocolate sauce. Serve immediately.
Yield: 1 quart, 4 to 6 servings