Cook onion in 1 tablespoon butter and olive oil in a medium skillet over medium heat 5 minutes, stirring frequently; cover, and cook 5 minutes. Uncover, and cook 3 more minutes or until soft and golden. Set aside.
Beat cream cheese at medium speed with an electric mixer. Stir in mayonnaise and next 4 ingredients. Fold in caramelized onion and salmon. Cover and chill.
Cut bread loaf in half lengthwise. Brush both sides with melted butter. Heat a large, heavy skillet over medium heat until hot. Place one half of bread in hot skillet, cut side down, and place a smaller heavy skillet on top of bread. Apply pressure to flatten bread. Cook 1 to 2 minutes or until toasted and browned. Turn bread and repeat. Repeat with remaining bread half. Cut bread into small triangles. Serve with dip. Garnish, if desired.