Prepare all ingredients at room temperature. Mash the banana and chop the pecans.

Make the pecan crumble first. Combine all crumble ingredients in a bowl and mix with gloved hands until clumps form.

Place the crumble mixture in the refrigerator or freezer to chill briefly.

Start the muffin batter. Preheat the oven to 180°C (356°F). Cream the room-temperature butter until smooth, then add sugar and salt and whip thoroughly.

Add the egg in 2–3 portions, whipping well after each addition until the mixture increases in volume.

Sift the dry ingredients (cake flour and baking powder) and fold them into the batter using a spatula.

Add the mashed banana and mix gently.

Add the chopped pecans and finish mixing the batter.

Fill muffin tins 70–85% full with batter.

Top the batter with the chilled pecan crumble and bake in the preheated oven for 20–25 minutes.