Preheat your oven to 275°F / 135°C. Prepare two 10-inch cake pans by greasing them with butter and dusting with flour (use a gluten-free flour blend to keep the recipe fully GF).
In a large, clean glass or metal bowl, beat the egg whites with an electric mixer on medium speed.
Once they become foamy, gradually add 1 cup (240 ml) of the confectioners' sugar and continue beating until the mixture holds soft peaks.
Sift the remaining 1 cup (240 ml) of confectioners' sugar with the cornstarch.
Add this mixture to the egg whites along with the almond extract. Increase the mixer speed to high and beat until the meringue is stiff, glossy, and holds firm peaks.
Gently fold the ground almonds into the stiff meringue using a large spatula. Use a light touch to avoid deflating the mixture.
Divide the meringue batter evenly between the two prepared cake pans.
Spread it carefully into a flat, smooth layer.
Bake for 1½ hours, or until the layers are a pale golden color and have started to shrink away from the sides of the pans.
Turn off the oven and let the layers cool slightly in the pans for 10-15 minutes.
Carefully run a knife around the edge of each pan and invert the layers onto wire racks.
Let them cool completely.
To assemble, place one cooled meringue layer on your serving plate.
Spread a little more than half of the lemon filling evenly over the top. Gently place the second layer on top.
Spread the remaining lemon filling over the top layer, leaving the sides of the bottom layer exposed for a rustic look. Decorate with a few blanched almond halves or create simple swirls in the filling with a knife.
Chill the torte in the refrigerator for at least one hour before serving to allow it to set.
When folding in the ground almonds, use a gentle figure-eight motion with a spatula to incorporate them without knocking the air out of the meringue.