Preheat oven to 325 F and prepare a baking sheet with parchment paper. In a mixing bowl, use a handheld mixer to beat the peanut butter, sweetener and baking soda until well combined. Add in the egg and vanilla extract and continue mixing until incorporated. Fold in the chocolate chunks but reserve a few for topping.
Press the dough into a pan prepared with parchment paper. I used an 8x10 inch pan, use a 6x6 inch pan for thicker bars. Bake for 10-12 minutes. Remove and top with more chocolate chunks if desired. Let cool for at least 20 minutes before serving. Sprinkle with fancy salt if desired.