Preheat oven to 400 degrees F. Grease a 15x10x1-inch baking pan; set aside. In a large bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Add the powdered sugar. Beat until combined, scraping bowl occasionally. Beat in the egg and orange flavoring until combined. Beat in the flour.
Press dough onto the bottom of the prepared baking pan. Using your thumb, make 54 indentations in the dough (9 rows of 6 thumbprints across). Fill each indentation with a scant 1 teaspoon preserves.
Bake in the preheated oven for 20 minutes or until edges are light brown. Cool in pan on a wire rack. Cut baked mixture into squares.
In a medium microwave-safe bowl, microwave white chocolate pieces on 100 percent power (high) for 1 to 1-1/2 minutes or until pieces are just melted, stirring after every 30 seconds (do not overcook). Spoon melted white chocolate into a small resealable plastic bag. Seal bag; snip off a small corner of the bag. Drizzle melted white chocolate over each cookie. Let cookies stand until chocolate is set. Makes 54 cookie squares.