Melt 1/2 cup butter in a large skillet; add onion, and sauté until golden brown. Add chicken livers and mushrooms. Cook, stirring frequently, 5 minutes or until livers are tender. Add remaining butter, seasoned salt, pepper, and lemon juice; stir until butter melts. Cool.
Divide mixture into 4 equal portions. Combine 1 portion of liver mixture with 2 egg quarters in container of an electric blender; process until very smooth. Transfer to a mixing bowl. Repeat procedure with remaining portions of mixture, blending each portion separately. Stir nuts into liver mixture, and mix well.
Press pâté in miniature molds. Cover and chill 8 hours or overnight; unmold. Serve on melba toast rounds.