Sous Vide Steak Sandwich

Ingredients

• 1 1/2 lb (680 g) flank steak
• Kosher salt and freshly ground black pepper
• 2 tbsp (30 mL) of extra virgin olive oil
• 1/4 cup (59 mL) sour cream
• 1/4 cup (59 mL) mayonnaise
• 1 tbsp. (15 mL) prepared horseradish, plus more to taste
• 1 large baguette, or 2 demi baguettes
• 4 oz (28 g) baby arugula
• 1 tbsp. (15 mL) freshly squeezed lemon juice
• 1/2 cup (118 mL) pickled onions