Preheat oven to 350°F.

Beat butter and sugar in a large bowl until light and fluffy.

Add egg and vanilla and beat to combine.

Whisk together flour, baking powder, and salt. Add to creamed mixture and beat until just combined. Dough will be slightly crumbly.

Divide dough into 4 equal portions and press each together. On a lightly floured surface, roll each portion of dough to a log 12 inches long.

Place logs on 2 ungreased cookie sheets (2 logs per sheet about 3 inches apart). Use your finger to to make an indention in the top of each log about 1/2-inch wide and 1/4-inch deep.

Place dulce de leche in a plastic zip top bag. Cut a corner from the bag. Squeeze dulce de leche from bag to pipe 2 tablespoons into the indention on each log.

Bake for 18 to 20 minutes, or until light golden.

Cool logs on cookie sheets for 2 minutes. Use 2 spatulas to carefully lift logs to a cutting board.

Slice logs diagonally into 3/4-inch wide strips. You may need to scrape dulce de leche off sides of the knife as you are cutting.

Place cookie strips on a wire rack to cool completely.