The filling: Blend the apple, butter and sugar with your fingertips and pour into a large microwave-safe cup.
Cover the cup with cling film and pierce it with a fork or a knife with a few holes. Cook for 1 minute at 800W in the microwave.
If there is some liquid in the preparation, drain slightly. Then add the precooked blackberries and mix.
The crumble: in a small bowl, mix butter, flour, honey and salt with your fingertips to obtain a paste with a sandy consistency.
Crumble the crumble on the fruit mixture, in the cup, and cook for 1 minute and 30 seconds at 800W in the microwave.