Preheat the oven to 325 F. Line an 8-inch square pan with parchment, or grease the pan, and set aside.
If the nut butter is not easily stir-able, gently warm it until it softens.
In a bowl, stir all ingredients very well so everything is fully incorporated and there are no clumps of baking soda.
Transfer the batter to the prepared pan and smooth the top with a spatula or a second sheet of parchment; remove the second sheet if used.
If desired, press additional chocolate chips or dried fruit into the top.
Bake on the center rack for 13 minutes (increase to 15 minutes if using almond flour); the bars should look slightly underdone when removed.
Let the pan sit for 30 minutes for extra gooey bars, or cool and rest overnight for firmer, set cookie bars.