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1
Preheat the oven to 350 degrees F. Line a 10 by 14 1/2-inch sheet pan (with sides) with parchment or waxed paper.
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2
In a mixer fitted with a paddle attachment (or using a hand mixer), cream the butter until soft and smooth.
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3
Add the brown sugar and mix until incorporated.
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4
In a separate bowl, stir together the flour and cornstarch.
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5
Add to the butter mixture and mix at low speed just until the ingredients are incorporated and the dough comes together.
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6
Turn the dough out onto a floured work surface and knead it 5 to 10 times, just to smooth the dough.
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7
Reflour your work surface.
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8
With a rolling pin, roll the dough out to fit the sheet pan.
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9
To transfer to the sheet pan, roll the dough up onto the rolling pin, lift it up, and unroll into the pan.
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10
Using light strokes of the rolling pin, roll the dough evenly into the corners and edges of the pan, and roll out any bumps.
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11
(Or, press the rolled-out dough thoroughly into the pan with your fingers.)
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12
Prick the shortbread all over with a fork to prevent any buckling or shrinking.
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13
Bake in the center of the oven for 15 minutes.
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14
After 15 minutes, rotate the pan and knock it once against the oven rack, to ensure even cooking and a flat surface.
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15
Bake 10 to 15 minutes more, until very lightly browned.
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16
Immediately sprinkle the granulated sugar evenly over the surface.
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17
Let cool 10 minutes, then cut into 1 1/2 by 3-inch bars.
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18
Let cool completely in the pan, then store in an airtight container.
