3/4 cup all-purpose flour
2/3 cup confectioners’ sugar
3 tablespoon unsweetened cocoa powder, American-style or Dutch-process
3 ounces semisweet or bittersweet chocolate (50-72% cacao), coarsely chopped, plus 2 1/2 ounces chopped into mini chip-size pieces, divided
1 1/2 tablespoon canola oil
1/4 cup granulated sugar
1 1/2 tablespoon light corn syrup, blended with 3 tablespoons lukewarm water
2 teaspoons vanilla extract
1/8 teaspoon salt
1 large egg
1/3 cup chopped toasted walnuts, (see Tip), optional