Make cashew praline: In a heavy skillet cook 1/2 cup sugar with 2 tablespoons water and a pinch of cream of tartar over moderately high heat, washing down any undissolved sugar that clings to the sides of the skillet with a brush dipped in cold water, until the mixture is a light caramel. Stir in quickly 1/2 cup finely chopped raw cashews. Pour the praline onto a buttered piece of foil and with a buttered spatula spread it into a thin sheet. Let it cool until it hardens and chop it coarsely.
In a bowl beat 1 stick or 1/2 cup butter with 1/3 cup sugar until it is creamy. Beat in 1 egg yolk and 1/2 teaspoon vanilla. Stir in 1 cup flour and two-thirds of the chopped praline and form the mixture into a dough. Form the dough into cylinders 2 1/2 inches long and 3/4 inch wide and put them about 2 inches apart on a lightly buttered cookie sheet. Sprinkle the cylinders with the remaining praline and bake them in a moderate oven (350° F.) for 12 to 15 minutes, or until they are lightly browned. Let the cookies cool on the sheet for about 1 minute and with a spatula remove them to a rack to cool completely. Makes about 18 cookies.