To make the cake, preheat the oven to 350°F. Grease an 8x8x2-inch pan with cooking spray, or softened butter. Line the bottom with parchment paper.
In a large mixing bowl, combine the sugar and zest and using your fingers, rub the zest into the sugar until fully incorporated. Add the extract and oil and whisk again. Add the egg and yolks, one at a time, whisking between each addition. Add the juice and the sour cream, whisking a final time toincorporate.
Sift the flour, baking powder and soda, and salt onto a sheet of parchment paper. Using the paper as a funnel, pour the dry ingredients into the wet in three additions, folding gently with a flexible spatula after each (alternatively, you can sift directly into the bowl of wet ingredients in three installments).
Transfer the batter to the prepared pan and bake for 30 to 33 minutes, rotating at the halfway point, until a toothpick inserted in the center comes out with a moist crumb or two.
Set the pan on a cooling rack and let the cool for 10 to 15 minutes. Invert the cake right side up on to the rack and place it in a baking sheet with sides.
To make the glaze, place the confectioners’ sugar and the lemon juice in a small bowl and whisk vigorously until smooth. Gently pour the glazeover the cake, spreading it with an offset spatula so it drips over the edges. Let the cake cool to room temperature before serving.
The cake is incredibly moist and will keep tightly wrapped in plastic wrap on the counter for 3 to 5 days.
Gluten free note: I use all purpose gluten free flour in place of the regular flour.