Preheat the oven to 350ºF and prepare an 8" baking dish by greasing it and lining it with a parchment paper sling.

Melt butter and dark chocolate using a double-boiler method: Bring a small saucepan of water to a boil with heatproof bowl over the top. Add the butter and chocolate to the bowl and slowly melt and stir the chocolate until all of it has melted. Remove from heat, let sit a few minutes and then whisk it all together. Alternatively you could melt them together in the microwave at 20 second intervals, whisking in between until it's fully melted.

Add ripe avocado to a food processor and blend until smooth. Add in eggs, maple sugar, cocoa powder, baking powder, maple syrup, vanilla extract and sea salt and blend until smooth, scraping down the sides as necessary.

Add the slightly cooled chocolate mixture to the processor and pulse until fully combined.

Transfer brownie batter to the prepared baking dish and smooth over the top.

Bake for 25 minutes or until a toothpick inserted in the middle comes out clean.

Cool completely before slicing.