Easy Slow Cooker Beef Stroganoff

Ingredients

• 2 pounds beef sirloin steak, thinly sliced
• 3 tablespoons olive oil
• 1 cup water
• 1 (1 1/2 ounce) packet beef stroganoff seasoning for the slow cooker (made by McCormick)
• 1 pound sliced baby portobello mushrooms
• 1 small onion, chopped
• 3 tablespoons butter
• 1/4 cup port wine
• 2 teaspoons dry mustard
• 1 teaspoon sugar
• 1 1/2 cups sour cream