<http://schema.org/recipeInstructions>
" Preheat oven to 350 degrees F. In large bowl, with mixer on low speed, beat butter, sugar, cocoa, and salt until creamy. Beat in egg yolk and vanilla until well blended, scraping side of bowl occasionally. Beat in chocolate. Add flour and beat until combined. In small bowl, with fork, beat egg white lightly to break up. Spread walnuts on plate. Roll dough by rounded measuring teaspoons into 1-inch balls. Coat balls lightly in egg white, letting excess drip off. Roll in walnuts to coat. Place cookies, 1 1/2 inches apart, on 2 large ungreased cookie sheets. Press thumb into center of each to make indentation. Bake cookies 8 minutes, switching sheets on racks halfway through baking. Fill each with 1/4 teaspoon preserves. Bake 8 to 10 minutes longer, or until jam is bubbly. Let cool on cookie sheets 2 minutes before removing with spatula to wire racks to cool completely. Store cookies in airtight containers at room temperature up to 3 days."^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.goodhousekeeping.com/food-recipes/a13635/chocolate-walnut-thumbprints-recipe-ghk1212/>