Cream butter in a large bowl with an electric mixer. Add in sugar or sweetener of choice and continue to beat until light, fluffy and thoroughly mixed.
Mix In vanilla extract, baking soda and salt. Add in the egg and mix until just incorporated. The mixture will appear slightly 'broken' (i.e. not thoroughly smooth, and thats totally ok). Mix in the almond or peanut butter and beat until thoroughly incorporated. If your mixture is too runny now (depends on how liquid your nut butter was), wait to add the chocolate chunks post chilling (or they'll sink to the bottom..!).
Cover with cling film and refrigerate for 1 hour, meanwhile preheat oven to 350°F/180°C.
Using an ice cream scoop or large spoon, scoop out the cookie dough. Place in a baking mat or parchment paper lined baking tray. Add in chocolate chunks and flatten slightly (see pictures for reference). Freeze for 15 minutes prior to baking.
Bake for 8-10 minutes (I did 7), until they just begin to brown around the edges (but be sure to not let them brown if you like them gooey!). Sprinkle with flaky sea salt (totally optional, but always *highly* suggested).
Store in an airtight container for 4-5 days. Though feel free to freeze the shaped dough and bake straight from the freezer (adding a few minutes to baking time) for fresh cookies on demand.
*If keto and using a sweetener such as erythritol, I like to use 1/2 cup (and 2/3 cup with allulose).Please note that nutrition facts were calculated using natural homemade peanut butter (i.e. peanuts processed until smooth in the food processor!) and erythritol as the sweetener (needless to say, if using sugar the carb count will be higher). Also note that the chocolate is not included in the nutrition facts (values vary widely). But if you use a bar of Lily's dark chocolate, add roughly 0.75g net carbs per cookie (so each cookie would be roughly 1.75g net carbs).