In a large bowl, cream butter and confectioners' sugar until light and fluffy. Beat in the vanilla. Gradually add flour; stir in hazelnuts.
Press into a greased 11-in. fluted tart pan with removable bottom. Bake at 400° for 10 minutes. Remove from the oven; reduce heat to 350°.
Spread apricot preserves over crust. In a large bowl, combine the hazelnuts, sugar, flour, butter and egg. Spoon over preserves. Arrange pear slices over filling in a concentric circle, slightly overlapping slices.
Bake for 40-45 minutes or until golden brown. Cool on a wire rack. Store in the refrigerator.