Preheat your oven to 350ºF. Pulse the flour, powdered sugar, 2 tablespoons corn starch and 1/4 teaspoon salt in a food processor just until combined. Add the butter pieces and pulse until the mixture is the texture of coarse meal, 7-8 pulses. Drizzle the canola oil and pulse again until the flour mixture is moistened and crumbly, about 5-7 pulses.
Coat an 8x8 inch baking pan with cooking spray and press the flour mixture into an even layer on the bottom of the pan. Avoid pressing the mixture too hard into the pan to avoid a dense, tough crust.
Bake at 350ºF until the crust is just lightly browned all over, about 25-30 minutes. Remove from the oven and cool to room temperature.
Combine the granulated sugar, orange-lemon juice, 3 tablespoons corn starch and 1/4 teaspoon salt in a sauce pan. Bring to a boil over medium heat, stirring constantly. Cook until thickened, about 2-4 minutes, depending on your heat.
Place the egg yolks in a medium bowl and carefully whisk in the orange-lemon liquid. Add this mixture back to the remaining orange-lemon liquid in the sauce pan and whisk to combine. Bring to a boil over medium heat making sure to whisk constantly. This may take a few minutes depending on your heat.
Remove from heat, whisk in the Aperol and pour the liquid through a fine mesh strainer into a bowl (discard the solids). Pour the orange-lemon mixture into the cooled shortbread crust and chill until set, three to four hours. (See Note) Dust with powdered sugar and cut into 16 squares before serving.
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