This recipe originally came from a newspaper clipping now yellowed with age. The cookies are delicate and delicious.
Stir together the flour, baking powder, and salt. In a large bowl, cream the butter and sugar. Add eggs, beating well. Beat in the zest and juice. Gradually add flour mixture, then stir in oats. Chill dough thoroughly (for at least 2 hours). Roll level tablespoonfuls of dough into balls and place onto greased cookie sheets, allowing room for cookies to spread. Using a flat-bottomed glass or custard cup that has been greased and dipped in sugar, flatten each ball to a ¼-inch thickness (dip the glass in sugar each time). Bake at 375 degrees F for 8 to 10 minutes, or until lightly browned around the edges. Cool for 1 minute, then carefully remove from cookie sheets and cool on racks.