Coarsely chop pecans. In a skillet melt butter over moderate heat until foam subsides. Toast pecans in butter, stirring occasionally, until golden and fragrant, about 5 minutes, and sprinkle with salt to taste. Cool pecans and chill in a sealable plastic bag. Buttered pecans may be made 3 days ahead and chilled.

In a heavy saucepan bring cream, milk, maple syrup, and salt just to a boil, stirring occasionally. In a bowl beat yolks until smooth. Add hot cream mixture to yolks in a slow stream, whisking, and pour into pan. Cook custard over moderately low heat, stirring constantly, until a thermometer registers 170° F. Pour custard through a sieve into a clean bowl and cool. Stir in extract. Chill custard, its surface covered with plastic wrap, at least 3 hours, or until cold, and up to 1 day.

Freeze custard in an ice-cream maker. Transfer ice cream to a bowl and fold in chilled pecans. Transfer ice cream to an airtight container and put in freezer to harden. Ice cream may be made 1 week ahead.