Heat oven to 350 F. Grease and line an 8 x 8 inch square baking pan with parchment paper.

In the bowl of a food processor, combine butter and dry ingredients. Pulse to combine until the mixture forms a ball.

If you don't own a food processor, bring the butter to room temperature and beat the room temperature butter and dry ingredients together in the bowl of a stand mixer using the paddle attachment, or in a large bowl using a rubber spatula or a hand mixer.

Remove 2/3 of the dough from the food processor and press dough into the bottom of the prepared pan in an even layer.

Bake until the crust is just starting to turn light brown, roughly 15 minutes.

Remove the crust from the oven and cool in the freezer for 10 minutes. This will make it easier to spread the Nutella over the top.

Heat the Nutella slightly to make it easier to spread. Pour the slightly melted Nutella over the top of the cooled crust, using an offset spatula to spread. You should have a thick layer of Nutella. Feel free to add more to taste.

Crumble the remaining top layer of cookie dough over the top of the Nutella.

Return to oven. Bake bars until the topping is crisp and golden brown in color, roughly 30 minutes.

Remove to a wire rack and let fully cool to room temperature.

Once cooled, dust the top of the bars with powdered sugar. Slice into 9 large servings, or 16 small servings.

Bars keep perfectly in an airtight container or wrapped tightly in plastic wrap for several days.