Preheat the oven to 350 degrees F and line a baking sheet with parchment paper.
Add the butter and sugar-free brown sugar to a stand mixer (or mixing bowl if using an electric hand mixer) and beat on medium-high speed until combined and fluffy.
Use a rubber spatula to scrape the sides of the mixing bowl, then add the eggs and the vanilla extract. Beat until the wet ingredients are combined and creamy. Again, scrape the sides of the mixer with a rubber spatula.
Stir together the remaining dry ingredients in a bowl and pour it into the mixer. Beat on medium-high until the dough is very well combined, thick, and sticky. IF the dough seems too wet or sticky, refrigerate it for at least one hour prior to baking.
Scoop the cookie dough onto the parchment-lined baking sheet, making any size cookies you like. The cookies will spread during the baking process, so give the dough balls plenty of room to expand. Bake for 8 to 13 minutes, depending on the size of your cookies. For regular sized cookies, go with 8 to 11 minutes, and for larger cookies, bake for 11 to 13 minutes, or until the edges are golden brown.
Remove the cookies from the oven and allow them to cool for 10 minutes before serving.
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Notes
*You can replace the oat fiber with 1/2 cup to 2/3 cup of quick oats if you don't mind adding some carb to the cookies. You can also replace it with 1/2 cup of additional almond flour if you don't mind losing the oat flavor.