Preheat the oven to 350F (180C). Butter the sides and bottom of an 8-inch (20 cm) square baking pan. Line the pan with parchment paper.
In a large bowl add the eggs and honey and whisk to combine.
Add vanilla extract, peanut butter or vegetable oil and mix to combine.
Add the buttermilk and continue mixing until combined.
Add the salt, baking powder, cocoa powder and oats and mix well to combine.
Fold in the ⅓ cup (60g) chocolate chips or chunks.
Pour the batter into the prepared pan. Sprinkle the remaining chocolate chips or chunks over the top.
Bake for 40-45 minutes until a toothpick inserted into the center comes out clean.
Let cool slightly before serving.