1Heat oven to 350°F. In medium bowl, stir together flour, baking powder, salt and allspice until blended; set aside. In large bowl, beat melted butter, brown sugar and granulated sugar with electric mixer on medium speed 2 minutes or until light and creamy. Add egg and 1 teaspoon maple flavoring; beat on low speed until blended. Add flour mixture; beat until soft dough forms. Stir in nuts and chocolate chunks.
2Onto ungreased cookie sheets, drop dough by rounded measuring tablespoonfuls 1 inch apart. Bake 9 to 11 minutes or until edges are light brown. Cool 1 minute; remove from cookie sheets to cooling racks.
3In medium bowl, stir together half-and-half, 2 tablespoons butter, the corn syrup, 1 teaspoon maple flavoring and 1/4 cup powdered sugar until blended and smooth. Slowly stir in 1 1/2 cups powdered sugar until blended. If necessary, stir in remaining 1/4 cup powdered sugar, 1 tablespoon at a time, until smooth and desired spreading consistency. For each cookie, spread about 1 1/2 teaspoons frosting almost to edge; let stand until set. Store in airtight container.