For the Cookie Base: Using an electric mixer, cream the butter and sugar together until light and fluffy. Then scrape the bowl and add the egg and vanilla. Beat again to combine. Then with the mixer running, slowly add the flour, baking powder, and salt. Scrape the bowl and beat again until smooth.
Dump the cookie dough out onto the prepared baking sheet. Use your hands to press the dough out evenly from corner to corner. Bake for 8 minutes.
Meanwhile, scoop both cans of dulce de leche into a microwave-safe bowl. Microwave for 1-2 minutes until very warm. Then mix in the nuts, flour, and cinnamon. Mix well to avoid clumps.
Carefully spread the nuts mixture evenly over the surface of the cookie base. Press it down a little to even out the filling. Place the pan back in the oven and bake for 18-20 minutes, until golden on top. Once cooled, pull the whole sheet out of the pan by the edges of the parchment paper and cut into bars.