Preheat the oven to 350ºF. Butter and line your 9x13 pan with parchment paper. Then butter the parchment paper to prevent sticking.
In a medium mixing bowl, whisk together the flour, powdered sugar, and salt for the shortbread crust. Cube the butter and work it into the dry mix until it all clumps together.
Press the dough into your prepared pan. Bake for 20 minutes until slightly golden.
Cool completely.
In a clean medium mixing bowl, whisk together the eggs and sugar for the filling until the mixture turns a paler yellow, and there are no longer streaks of egg white. You want the eggs very well incorporated.
Whisk in the zest, cinnamon, and clove to distribute, and then stream in the orange juice.
If your filling is frothy, pour it through a mesh strainer over your prepared shortbread crust.
Bake for 20-25 minutes until the filling is just set.
Allow to cool in the pan for 10 minutes until the pan is cool enough to touch. Then, use a knife to run along the edges of the pan to make removal easier. Using the parchment edges as handles, remove the spiced orange bar to a cooling rack to finish cooling completely.
Once cooled, cut your bars into 24 squares and dust thoroughly with powdered sugar.