How to Make It
Combine the cream cheese and gruyere in the bowl of a food processor; process until smooth.
Heat oil in a large skillet over medium heat. Add onion, sugar, salt, and pepper to pan, stirring frequently until liquid is released and onions are opaque. Stir in sherry vinegar to deglaze pan; remove from heat and cool to room temperature.
Stir onion mixture and onion soup mix into cheese mixture; mix until evenly incorporated. Scrape cream cheese mixture onto a parchment paper-lined baking sheet.
Using lightly moistened hands, shape cream cheese mixture into a ball. Wrap in plastic wrap and refrigerate for 45 minutes to 1 hour, or until it can be easily rolled.
Coarsely chop about 1/2 of the baguette into pieces; reserve remaining half for serving. Place chopped baguette in the bowl of a food processor; pulse until fine crumbs form. Heat a cast-iron pan over medium-high; add butter to pan. Once melted, stir in the baguette crumb; cook, stirring frequently, until golden brown, about 5 minutes. Toss bread crumbs with thyme.
Spread bread crumb mixture evenly on a rimmed baking sheet. Roll the cheese ball in the crumb mixture to evenly coat.
Place cheese ball on a serving platter; serve with additional sliced baguette.