Preheat your oven to 350°F (175°C) and prepare a 9-inch springform pan by lightly greasing it or lining with parchment paper.

In a large mixing bowl, combine all-purpose flour, cocoa powder, baking powder, baking soda, and salt. Whisk together until well-blended.

In a separate bowl, mix together granulated sugar and vegan milk until fully dissolved. Whisk for a smooth consistency.

Gently pour the wet mixture into the bowl of dry ingredients and mix until just combined, being careful not to over-mix.

Transfer batter into the prepared springform pan and bake for 20 minutes, or until a toothpick comes out clean.

Once baked, cool the cake in the pan for 10 minutes, then remove and place on a wire rack to cool completely.

In a bowl, whip vegan heavy cream until soft peaks form, then fold in melted vegan chocolate chips until combined.

Slice the cooled cake horizontally into two equal layers. Spread half of the mousse on one layer, then top with the second layer and spread the remaining mousse.

Refrigerate the cake for at least 3 hours to let flavors meld.

Melt vegan chocolate chips and vegan butter in a saucepan over low heat, stirring until smooth. Let cool slightly.

Pour the ganache over the mousse cake and refrigerate again for about 30 minutes to set.

Slice the cake carefully and serve chilled.