For the cookie: Mix powdered sugar and butter in a 2 1/2 quart bowl; stir in vanilla and egg. Stir in flour, cocoa, baking soda and cream of tartar. Refrigerate until chilled, 2-3 hours.
Heat oven to 375 degrees.
Prepare peanut butter filling: Mix creamy peanut butter and butter. Gradually stir in 1 cup powdered sugar.
Divide cookie dough in half. Roll each half into a rectangle about 13 1/2x9 inches, on well-floured cloth covered board. Cut each into strips that are 1 1/2x9 inches.
Shape peanut butter filling into 18 balls (1 1/4 inch). Roll each ball into a rope, 9 inches long, on a floured surface.
Place ropes on centers of chocolate strips. Bring long edges of each strip over filling; seal well.
Shape into pretzel on ungreased cookie sheet.
Bake until set, 8-10 minutes; cool.
To make the cocoa glaze: Mix powdered sugar and cocoa. Stir in 2 tablespoons milk until smooth. If necessary stir in additional milk, 1/2 teaspoon at a time, until of desired consistency.
To make peanut butter filled logs: Do not shape into pretzels. Cut each 9-inch peanut butter chocolate strip into 3 logs (3 inches long). Bake on ungreased cookie sheet for 7-8 minutes. (4 1/2 dozen logs).