Preheat the oven to 400F and line 2 baking trays with parchment paper.
Sift the flour and cornstarch together and set aside. Whip the egg yolks with 3 tbsp of the sugar until thick and pale and they hold a ribbon when the beaters are lifted. In a separate bowl, whip the egg whites with the cream of tartar until foamy, then slowly add the remaining 6 tbsp of sugar and continue whipping until the whites hold a medium peak when the beaters are lifted.
Fold the whites into the yolk mixtures using a whisk, then fold in the flour until just incorporated. Fill a piping bag fitted with a plain tip. Pipe a spiral of batter, following the circle and pipe spiraling inward to fill the circle. On the second baking tray, pipe 18 to 22 ladyfingers about 3 inches long. Bake for about 8 minutes (the circle of batter will take about 10 minutes) and allow the ladyfingers to cool on the tray before lifting off.
For the lemon mousse, bring the lemon juice and 1/2 cup of the sugar up to a simmer. In a separate bowl, whisk the egg yolks with the remaining 1/2 cup of sugar. Slowly pour the lemon syrup into the eggs while whisking and then return the entire mixture to the pot. Whisk this over medium heat until it just begins to bubble, about 2 minutes, then remove this from the heat and whip with electric beaters or in a stand mixer until cool. Add the butter and zest and beat in until smooth.
Whip the cream to a soft peak and fold this into the lemon mixture in two additions.
To assemble the torte, place the disc of ladyfinger cake in the bottom of an ungreased 9-inch springform pan. Trim bottom of the lady fingers so they can stand upright around the inside edge of the pan, and so that they are the same height as the pan (2-inches). Arrange these in the pan. Spread a 1-inch layer of mousse over the cake and arrange half of the raspberries overtop. Spread the remaining mousse over the berries and use an offset spatula to ensure the mousse is level. Chill the torte for at least 4 hours.
To serve, remove the springform ring from the pan and slide the torte onto a serving platter. Arrange the remaining 1 cup of raspberries on top of the torte and serve.