Make flax eggs by whisking together 2 tablespoons ground flaxseed and 6 tablespoons water in a small bowl. Let rest 5 minutes before using.
In a medium mixing bowl, stir together the melted coconut oil, white sugar, and brown sugar.
Add the flax eggs, vanilla, and cocoa powder Stir until well combined.
Slowly mix in the all-purpose flour and baking soda, adding the flour ½ cup at a time. The dough should be firm enough that it can be rolled into a ball but still a little wet.
Cover and chill the dough in the fridge for 30 minutes. Preheat the oven to 350F and line a cookie sheet with parchment paper.
Roll cookie dough into walnut-sized balls, about 2 tablespoons each. Use your finger to hollow out the center.
Put a heaping ½ teaspoon peanut butter in the center hollow of each dough ball.
Pinch the cookie dough edges together like a dumpling, or use a small piece of cookie dough to close the gap. Roll into a ball.
Place cookie dough at least two inches apart on a parchment paper lined baking sheet.
Bake at 350F for 9-11 minutes, until the edges are set. The center should still look a little underbaked. Sprinkle with flaked sea salt. Let rest 5 minutes before transferring to a rack to cool.
Coconut oil: Measure out the oil after melting. An equal amount of liquid at room temp oil can be used, such as canola or olive oil.
Peanut butter: Any kind works. If you're finding the peanut butter hard to work with, you can place ½ teaspoon scoops of peanut butter on a wax-paper lined dish and freeze them for just 15 minutes. This will make it a lot easier to place the peanut butter in the center of the cookie dough.
Flaked salt: If you don't have flaked sea salt, I recommend adding ⅛ teaspoon table salt to the cookie dough before baking.
Freezing: I recommend letting them cool to room temperature before transferring to an airtight container. Freeze for up to 3 months. They thaw quickly at room temperature or can be popped in the microwave for just 15 seconds.
Storage: These cookies are best stored at room temperature in an airtight container. For best quality, enjoy within 4-5 days.