In a food processor, blend cheese and butter. Add the egg, garlic salt and onion salt; process for 1 minute or until creamy. Spread 2 tablespoons on each slice of bread. Stack two slices of bread, cheese side up, for each sandwich; sprinkle with paprika if desired. Cut each sandwich in half diagonally. Place on an ungreased baking sheet. Bake at 400° for 12-15 minutes or until golden and bubbly.