Preheat the oven to 355 degrees F/180 degrees C. Grease a 9-inch/23 cm springform pan with cooking spray or brush with softened butter. Then cover the bottom and the sides of the pan with parchment. If allowed, instead, flour it.

Extra tip: if you use a regular cake pan, use precut circle cake pan liners (better than a circle of parchment paper) at the bottom of the pan to facilitate unmolding.

In a small saucepan, melt butter over low heat and let cool to room temperature. Or melt the butter in the microwave. In a large mixing bowl, beat the egg with sugar and salt with a balloon whisk for 1 to 2 minutes. Add the bitter almond extract and almond flour and mix until homogeneous.  Add the cooled melted butter and gently mix again.

Pour the batter into the prepared pan and bake in the center of the oven for about  15-20 minutes. Using the oven mitts, remove the pan from the oven and sprinkle the surface of the cake with flaked almonds. Then bake again for 15-20 minutes.

Check the cake's doneness: if the blade of a knife or a cake tester inserted in the center of the cake comes out almost clean, the cake is ready. Leave to cool in the mold to room temperature, then unmold. Let it cool completely on a wire rack and sprinkle with powdered sugar.