Combine flour, sugar, and salt. Cut in butter until mixture resembles fine meal. Spread 2.5 c of mixture in bottom of greased 11x7x2 inch pan. Blend soda and nutmeg into remaining mixture. Combine egg and sour cream. Stir into mixture until just blended. Spoon over crumb mixture and spread evenly. Sprinkle nuts on top. Bake 350 deg, 40 minutes.