Preheat oven to 175°C (350°F). Grease and line an 8-inch (20 cm) round cake pan with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. Set aside.
In a large mixing bowl, beat the softened vegan butter and granulated sugar together until light and fluffy (2–3 minutes with a hand mixer) or in the bowl of an electric mixer fitted with the paddle attachment.
Mix in the vanilla extract, almond extract, mashed banana and almond flour until well combined.
Add half of the dry ingredients to the wet mixture, stir gently with a spatula, then whisk in the milk. Finish by folding in the remaining dry ingredients just until all streaks of flour disappear, but don't overmix it. The batter will be thick.
Spread the batter evenly into the prepared pan and smooth the top with a spatula. Arrange the plum slices on top in a circular pattern or rows, pressing them lightly into the batter.
Bake for 50–55 minutes, or until a toothpick inserted in the centre comes out clean. (Check around 45 minutes if your oven runs hot.)
Let the cake cool in the pan for 10–15 minutes, then transfer to a wire rack to cool completely.
Dust with powdered sugar or brush with warmed apricot jam for a glossy finish.