Prepare Instant Pot with rack and a quart of water in pot. Set for sous vide (Ultra) for 1-1/4 hour at 182 F. Have flanera pan ready.

Caramel: put 1/2 cup sugar in a small saucepan with the water. Heat on medium, shaking the pan occasionally, but dont stir. Syrup will boil for a while until it starts to turn brown. Quickly remove it from the heat; turns dark very fast. Immediately pour into the flanera. DONT CLEAN PAN.

Flan: Measure milk in quart-sized measuring cup and heat in same saucepan with 1/2 cup sugar and lemon zest just until it reaches a boil then turn to low for 20 minutes. If no zest, no need for the 20 minutes

Meanwhile, break eggs in same measuring cup and whisk for a minute or two. Add vanilla. Whisk in hot milk, very slowly at first to temper the eggs. Pour back in pan and whisk to completely mix.

Pour milk mixture into flanera pan on top of the caramel. Cover and lock. Set in water in Instant Pot on rack. Water should reach only halfway up flanera. Hit START

Sous vide for 1-1/4 hour at 182 F. The custard is done when it has set, which you can verify by inserting a knife that comes out clean. If not, cook for another 15 mins. It should still wiggle a bit.

Carefully take flanera out of pot and cool completely in fridge with cover on. The longer in fridge the more likely the caramel will melt better.

To serve, remove lid, run knife around sides, place plate on top and flip over. Cut into wedges.

Similar to the faster pressure cook method but this way flan comes out more silky.