With the rack in the middle position, preheat the oven to 325°F (165°C). Line the bottoms of two 8-inch (20 cm) springform pans with parchment paper. Do not butter.
In a bowl, combine the flour and baking powder. Set aside.
In a large bowl, whisk together the egg yolks, 3/4 cup (160 g) of the sugar, the oil, lemon zest and juice, and salt. Set aside.
In a third bowl, beat the egg whites with an electric mixer until soft peaks form. Gradually add 1/2 cup (105 g) of the sugar and continue beating until stiff peaks form.
Stir the dry ingredients into the egg yolk mixture, then incorporate one-quarter of the meringue. Using a spatula, gently fold in the remaining meringue. Divide the batter between the prepared pans.
Bake for 40 minutes or until a toothpick inserted into the centre of the cakes comes out clean. Remove from the oven and immediately place them upside down on a wire rack. Let cool completely, about 3 hours. Run the blade of a knife between the cakes and pans, then unmould.
In a bowl, whip the cream and the remaining sugar with an electric mixer until stiff peaks form.
Slice each cake horizontally in half to obtain 4 layers.
Place 1 cake layer on a serving platter. Spread with one-quarter of the whipped cream. Repeat with the remaining cake layers and whipped cream, finishing with the whipped cream. Using a large offset spatula, smooth the surface of the cake. Garnish with the lemon confit slices and refrigerate until ready to serve. The lemon chiffon cake will keep for 2 to 3 days in the refrigerator.