Combine the flour with the baking powder, baking soda, salt and nutmeg. In a clean 1 quart-sized glass jar with a wide mouth layer the white sugar followed by the flour mixture. Press firmly in place and seal. Attach a card with the following instructions:
In a large bowl, beat 1 cup room-temperature butter until light and fluffy. Mix in 1 egg until combined. Add 1/2 cup sour cream and 1 teaspoon vanilla and blend at low speed. Gradually add contents of jar and mix until fully incorporated. Wrap cookie dough in plastic or foil and refrigerate for several hours or overnight. Remove dough from the refrigerator. Preheat oven to 375 degrees F (190 degrees C). Roll chilled dough out on a lightly floured surface and cut dough into desired shapes. Place on an ungreased cookie sheet and bake at 375 degrees F (190 degrees C) until edges are golden brown, 10 to 12 minutes.