To make the cake: Preheat the oven to 325°F (160°C). Butter and flour a 9-inch (23cm) springform cake pan or cake ring.
Using a stand mixer fitted with the whisk attachment, on medium speed, combine the eggs, granulated sugar, salt, vanilla, and lemon juice, beating until pale and fluffy, 3 to 4 minutes. Add the flour, mixing it in on low speed until smooth. Add the melted butter and mix briefly to incorporate. Pour the batter into the prepared cake pan.
Bake until the top is golden brown and cake springs back when pressed in the center, about 25 minutes. Transfer the pan to a wire rack and let cool for 5 to 10 minutes before releasing the springform (or ring). Dust the cake lightly with flour before inverting it onto the wire rack. Let cool completely.
To make the cream-peach filling: Prepare a water bath by bringing a pot of water to a simmer. In a bowl of cold water, soak the gelatin sheets until the sheets become limp, 5 to 10 minutes.
In the meantime, in a heatproof bowl, combine the quark, milk, and granulated sugar. Place the bowl over the pot of simmering water and whisk until the mixture is well com¬bined and lukewarm. Remove the bowl from the pot and set aside.
Gently pick up and squeeze the sheets of gelatin to get rid of excess water and transfer them to a medium bowl.
Ladle a third of the warm quark mix¬ture into the bowl with the gelatin and whisk together until the gelatin has melted into the quark and no lumps remain. Return the quark-gelatin mixture to the rest of the quark, and mix until fully combined. Stir in the vanilla and lemon juice.
In a medium bowl or using a stand mixer fitted with the whisk attachment, whip the cream to stiff peaks. Transfer a third of the whipped cream to the quark-gelatin mixture and whisk gently until light¬ened. Then, using a spatula, gently fold the remaining whipped cream into the batter.
Using a serrated cake knife, slice the cooled cake in half horizontally. Lay the cleaned cake ring or the spring¬form part of the cake pan onto a flat plate. Place the bottom of the cake into the ring.
Spread half of the quark mixture across the cake. Arrange the peach halves, pit-side up, evenly over the cream. Cover with the remaining quark mixture, then top with the remaining half of the cake. Refrigerate until set, at least 6 hours but preferably overnight.
Remove the springform or cake ring, sprinkle the cake with confectioners’ sugar, and slice. Serve immediately.
Meredith Erickson is the co-author of numerous cookbooks. She has written for the New York Times, Elle, Saveur, and Lucky Peach. When not hosting tours throughout the Alps, Meredith splits her time between Montreal and Milan.