Pour milk into pressure cooker pot. Lock pressure cooker lid in place. Set steam vent to Sealing. Press the Yogurt button until display reads “Boil”. When the cycle completes the screen will display “Yogt”. Remove lid and check that milk temperature is at least 180°F (if milk is lower than this, set pressure cooker to Sauté on Low until milk reaches temperature). Skim the "skin" from the surface of the milk and discard. Remove steel pot from the base of the pressure cooker and set into a large ice bath to cool the milk to 110°F (43°C), about 5 minutes. Remove pot from the ice bath and wipe the outside dry. Ladle one cup of milk into the small bowl with room-temperature yogurt; whisk until smooth. Stir yogurt mixture into the milk, being careful not to scrape the bottom of the pot. Return pot to pressure cooker base. Lock pressure cooker lid in place. Set steam vent to Sealing. Press the Yogurt button and cook for 10 hours. When the cycle completes, the display will read "Yogt". Line a fine-mesh strainer with cheesecloth; set over a large bowl. Pour yogurt into the strainer; refrigerate for at least 4 hours. Stir sugar and vanilla through the strained yogurt; divide into glass canning jars. Keep yogurt refrigerated for up to 2 weeks.