Combine the 200 grams crushed Marie biscuits with 60 grams melted butter in a large bowl. Press this mixture firmly into a 23cm pie tray (lined and greased), then place it in the refrigerator to chill.
In a flat frying pan, melt 50 grams butter with 40 grams sugar over low heat. Add the sliced bananas and stir lightly with a wooden spoon until they soften slightly. Take the pan off the heat and stir in 1 teaspoon rum, then let the mixture cool completely.
In a separate mixing bowl, whisk 1 egg with 35 grams sugar from medium to high speed until the mixture is thick and creamy. Lower the speed, then add the 1/2 lemon peel, 30 grams ground almonds, and 15 grams all-purpose flour, mixing until just combined. Finally, use a spatula to fold in the remaining 200 grams melted butter and 3/4 tablespoon lemon juice, mixing gently until smooth.