This is probably not the same one, but it is soft and very good (my fovorite).

3/4 Cup margarine
3/4 Cup sugar
3/4 Cup brown sugar
1 egg
3/4 Cup peanut butter
1 teaspoon vanilla
1 3/4 Cup flour
1/2 teaspoon baking soda
1/2 teaspoon salt
Granulated sugar for rolling

Cream margarine and sugars. Blend in egg, peanut butter and vanilla. Add combined dry ingredients. Mix well. Shape rounded teaspoonsfull of dough into balls. Roll in granualted sugar. (at this time I expect you could make your thumbprint).Place onungreased cookie sheets. Bake at 350 degrees for 10 - 12 minutes. Watch closely to be sure they don't burn. The original recipe said 375 degrees, but they burned in my oven at this temp. Hope you enjoy the cookies!