Preheat the oven to 350ºF. Grease a 9x9-inch baking pan with coconut oil and line with parchment paper. Set aside.
In a large bowl or in the bowl of a stand mixer fitted with the paddle attachment, add the eggs and coconut sugar. Whip on medium-high speed for 3 minutes until the mixture doubles in size and becomes light and fluffy.
Add the maple syrup, oat flour, cocoa powder, coffee, and vanilla extract and gently stir to combine.
Fill a medium saucepan with 1-inch of water and place over low heat until simmering. Place a heatproof bowl on top and add 1 1/4 cups chocolate chips with coconut oil. Allow the chocolate and coconut oil to melt and stir until combined and smooth. You can also do this in the microwave, heating at 30-second intervals until ingredients are melted and combined.
Pour a little bit of the chocolate mixture into the egg base and stir quickly to temper the egg mixture so the eggs don't curdle and cook.
After tempering with a little bit of the chocolate mixture, pour the remaining melted chocolate mixture into the egg mixture and gently fold to combine.
Add the remaining 1/4 cup chocolate chips and fold gently to combine.
Pour the batter into the prepared baking pan and bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and allow to cool completely in the pan on a wire rack. Slice and serve.
Tip: Make the oat flour by adding the rolled oats into the bowl of a food processor or a high-speed blender and pulsing until finely ground and the consistency of flour.