In a small sauce pan, beat 1 egg; add 1/2 cup milk and 2/3 cup sugar. Cook and stir over low heat for several minutes or until mixture begins to barely coat spoon. Add chocolate and stir until melted and mixture is thickened slightly. Cool to room temperature. In a bowl, cream butter until fluffy; add sugar and cream until light. Add vanilla and remaining eggs. Mix well. Sift together the dry ingredients and add alternately with remaining milk. Stir in mixture.
Spread half of batter into large round circles on a buttered and floured cookie sheet; repeat with remaining batter. Bake at 350 degrees for 20 minutes or until top springs back when lightly touched with a finger. Cool and remove ot rack for complete cooling. Place one layer on serving plate and spread with filling; top with other layer.
