Preheat the oven to 400 degrees F (200 degrees C).
Combine sugar and lemon zest in a bowl. Using your hands, rub zest into sugar to release the natural oils of the zest. Add flour and mix well.
Whip in buttermilk, lemon juice, eggs, butter, and lemon extract. Pour batter into pie crust.
Bake in the preheated oven for 10 minutes. Reduce heat to 350 degrees F (175 degrees C) and bake until center is slightly jiggly in center, 50 to 65 minutes. Custard will continue to set as pie cools.
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