Directions

1. Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with aluminum foil.
2. Cut a checkerboard pattern into the sourdough bread round by cutting 5 or more slices about 1 inch apart into the sourdough bread round with a serrated knife, taking care not to cut all the way through the loaf. Rotate the bread a quarter turn, and cut 5 or more slices going the other way, to finish the checkerboard pattern. The slices will still be attached at the bottom.
3. Melt the butter over low heat in a saucepan, and stir in the mustard, lemon juice, poppy seeds, seasoned salt, and onion until the mixture is well combined. Place the bread loaf onto the prepared baking sheet, and carefully pour the butter mixture all over the bread, including in the cracks between squares, letting the butter mixture soak into the bread. Stuff slices of Swiss cheese into the spaces between the bread squares.
4. Bake in the preheated oven until the cheese is melted and bubbling, and the loaf is browned, about 30 minutes. To serve, let guests pull the bread apart into individual squares.