In a small bowl, cream butter and brown sugar until light and fluffy. Beat in egg yolk and vanilla. Beat in flour until blended.
Press dough onto a greased 12-in. pizza pan; arrange pecan halves around outside edge of dough. Bake at 350° for 20-25 minutes or until lightly browned.
In a small bowl, combine the sour cream, brown sugar and vanilla. Immediately spread over hot crust to within 1/2 in. of pecan halves. Sprinkle with chopped pecans. Cool on a wire rack. Store in the refrigerator.