1. Preheat the oven to 390°F (200°C).
2. In a large mixing bowl, add the liquid from canned chickpeas (aquafaba) and whisk using an electric mixer until stiff peaks form. Whisk until it´s more than doubled in size, white and foamy.
3. Add a little flour and whisk, adding more and whisking until all flour is used.
4. Pour milk into the mixture and keep whisking.
5. Add cocoa powder, a pinch of salt, agave syrup, and melted butter. Whisk until combined.
6. Add chopped chocolate and stir with a spatula.
7. Pour cake batter into a 9 inch (22 cm) greased springform.
8. Bake in preheated oven for 15 minutes.
9. Dust with powdered sugar or serve with a scoop of dairy-free ice cream or coconut whipped cream.