Remove the Plant Butter from the fridge to come to room temperature. Whisk together the flaxseed meal with 6 tablespoons (85mL) water until well combined. Place in the fridge for 15 minutes to help it gel and set. This is your “flax egg.”
Meanwhile, prepare a double boiler to melt the chocolate and butter. Add a few inches of water to a saucepan and bring to a simmer. Nestle a large heatproof glass bowl that sits on top of the saucepan without touching the water to create a double boiler. Once the water is simmering, add the softened Plant Butter and the 9 ounces or 255g of the dark chocolate chips or chopped dark chocolate to the bowl. Stir frequently with a spatula until the mixture is just melted. Take off the heat and allow it to cool to room temperature.Alternatively, you can melt the chocolate and Plant Butter in a microwave-safe bowl and melt in 30 second intervals, stirring after each interval.
While the chocolate is cooling, whisk together the espresso powder with 2 tablespoons of water. Or, if using coffee, measure out 2 tablespoons very strongly brewed coffee.
Once the chocolate-butter mixture is cooled to room temperature, add the diluted espresso, sugar, vanilla, and flax eggs. Whisk until well combined.
In a medium bowl, mix together the flour, baking powder, and sea salt.
Using a fine mesh sieve, sift the flour mixture into the chocolate mixture, stirring until just combined. The batter should be relatively thin, like brownie batter more than cookie batter. Using a silicone spatula, fold in *almost* all of the remaining chocolate chips or chopped chocolate. Reserve a few pieces of the chocolate for the topping after the cookies have been baked.
Cover the batter and refrigerate it for 1 hour (or longer) to firm up. When you remove it from the fridge, allow it to rest at room temperature for 5 minutes before scooping.
Preheat the oven to 325°F/163°C. Line two half-sheet pans or large cookie trays with parchment paper. Use your hands to form large uniform-sized balls, about 4 tablespoons per cookie. Space them apart on the two sheet pans, no more than 6 cookies per sheet.NOTE: I made 12 large cookies, though we could have probably made 1 or 2 more cookies (we ate some batter).
If you can, return the pans to the fridge for 15-20 minutes. This prevents them from spreading as much when they’re baking.
Bake for 13-14 minutes, or until the edges look set but the center still looks a bit gooey. Remove from the oven and immediately sprinkle with flaky sea salt and the reserved chocolate chips or chopped chocolate. Allow cookies to rest for 5-10 minutes before transferring the cookies to cool completely on wire racks.