Step 1

Attach sous vide wand to stock pot. Fill pot with water according to manufacturer's instructions.

Step 2

Preheat sous vide wand to 183°F.

Step 3

In a small bowl, whisk together stock, lemon juice, lemon zest, mustard, shallots and brown sugar.

Step 4

Place blueberries, butter and beef stock mixture in a food-safe plastic bag and seal, removing as much air as possible.

Step 5

Submerge bag in water and set timer for 20 minutes.

Step 6

At end of cook time, carefully remove bag from water. Open bag and serve sauce over steak.