Heat A Large Skillet Over High Heat.
When Hot, Add 2 Tablespoons Butter, Onions, And Salt.
Sauté On High Until Extra Moisture Evaporates, About 2 Minutes, Then Reduce Heat To Medium-High And Cook Onions Until Dark Brown In Color, About 5 Minutes.
Remove From Skillet And Set Aside.
Assemble Each Sandwich With 1 Slice Of Swiss On One Piece Of Bread And 1 Ounce Brie On The Other.
Add ½ Of A Sliced Pear And Top With One-Fourth Of The Onions.
Top Sandwich With Another Piece Of Bread, And Butter Outsides Of Sandwiches With 1 Tablespoon Butter On Each Slice.
Return Skillet To Medium Heat.
When Hot, Add Sandwiches.
Cook Until Golden Brown, About 3 Minutes Per Side.
Serve Immediately.