Line an 8-inch square baking pan with parchment paper.
Beat the softened butter for 3–5 minutes, until light and fluffy. Gradually add the confectioners’ sugar and continue beating until smooth and pale.
In a separate bowl, whisk together the flour, Earl Grey tea, salt, and about three-quarters of the lemon zest.
Add the dry ingredients to the butter mixture and mix on low just until the dough comes together. Avoid overmixing.
Press the dough evenly into the prepared pan. Refrigerate for 30 minutes.
Preheat the oven to 300°F.
Rub the remaining lemon zest into the turbinado sugar with your fingertips, then sprinkle evenly over the chilled dough.
Score the dough into rectangles.
Bake for 45–55 minutes, until set and just lightly golden around the edges.
Cool completely in the pan, then cut along the scored lines.