To make the crumble topping in a medium bowl, place all-purpose flour, almond flour, icing (powdered) sugar, ground cinnamon, and salted butter cut into small cubes. Work with your hands to make the crumbly sand-looking dough. Add flaked almonds and combine. Refrigerate.

Heat oven to 300 degrees F/150 degrees C. Using a flour sifter, sift all-purpose flour with baking powder and set aside. Line a 24-cup mini muffin tin with mini muffin cups (aka mini baking cups). Or grease the cavities of the mini muffin pan with a cooking spray.

To make the muffin batter, place the softened butter and muscovado sugar in a large mixing bowl and beat for about 5 minutes, using an electric mixer. Add sifted dry ingredients, egg, and delicately mix with a rubber spatula. Mash bananas using a fork or a spoon and fold mashed bananas into the principal preparation. Add cognac and mix with a spatula just to combine (don't over mix). 

Divide batter evenly into the prepared mini muffin pan or a greased muffin tin. You can use a teaspoon or a medium ice cream scoop to scoop the batter. The last step is to sprinkle the chilled crumble topping over the batter. Finally, you can add a little bit of flaked almonds on top of each muffin.

Bake muffins in the preheated oven for 30 minutes. They are ready when a toothpick (a wooden pick) inserted into the center of a muffin comes out clean. Let them cool on a wire rack. Dust the muffin top with icing sugar if desired.