4 Bowls, 1 Tablespoon, 1 Hand mixer, 1 deep bowl, 1 Fine-mesh sieve, 1 Wooden spoon, 1 Baking sheet, 1 Parchment paper, 1 Rubber spatula, 1 Cutting board, 1 Small knife, 1 Citrus juicer, 1 Small pot, 1 baking dish, 1 Large knife, 1 Plastic wrap, 1 Ladle
1 Separate the eggs: Put the yolks in a bowl and the whites in a tall vessel. Add a pinch of salt and 5 tablespoons water to the egg yolks and beat until frothy with a hand mixer.
2 Add a pinch of salt to egg whites and beat until very stiff peaks.
3 Mix together the flour and baking powder in a bowl. Fold into the egg-yolk mixture with a wooden spoon.
4 Also add egg whites and fold in well.
5 Line a rimmed baking sheet or roasting pan with parchment paper. Put the batter on it and spread smooth with a rubber spatula. Bake on middle rack of preheated oven at 180°C (fan 160°C, gas mark 2-3) (approximately 350°F/approximately 325°F) until golden brown, about 12 minutes. Remove and let cool.
6 Meanwhile, soak the gelatin in a bowl of cold water until softened, about 10 minutes. Squeeze out the lemon juice.
7 Rinse peaches, halve, remove pits and chop coarsely. Toss in a bowl with a little lemon juice. Mix in the yogurt and maple syrup and season to taste with more lemon juice.
8 Pick over the raspberries and rinse if necessary.
9 Melt the dripping wet gelatin in a small saucepan over low heat while stirring. Remove from heat and stir in 3 tablespoons of the yogurt mixture. Then mix into the remaining yogurt mixture.
10 Turn out the cooled biscuit base onto a work surface and remove the parchment. Cut the biscuit in half and place in a rectangular shaped (about 18 x 30 cm) (approximately 8 x 12 inches) baking dish. Top with about half of the raspberries, then spread with half of peach-yogurt cream in a smooth layer. Place the remaining biscuit half on top and press it down slightly. Spread with the remaining yogurt cream and top with the remaining raspberries.
11 Finely chop the pistachios with a large knife and sprinkle over the casserole. Cover with plastic wrap and let set in the refrigerator for about 4 hours.