Beat together:

5 1/3 oz. unsalted butter
1 cup sugar

Add:

1 T. lime zest
1/2 tsp. salt
1/2 tsp. baking soda

Add:

1 egg
1 T. + 1 tsp. milk
1 tsp. lime juice

Add 2 cups pastry flour.

Bake at 325 on greased sheets until edges brown.