Sift together in bowl the flour, sugar, baking powder and salt. Add butter, 2/3 c. milk, lemon extract and vanilla. Mix with electric mixer on medium speed for 2 minutes. Add 1/3 c. milk and egg yolk. Beat two more minutes. Pour batter into two 8 inch round prepared pans. Bake at 350 degrees for 30-35 minutes. Cool and frost.