Peel and slice potatoes into thin strips and soak in water for 20 minutes.
In a medium bowl, whisk together eggs and seasonings until very frothy.
In a mixing cup, whisk together, tomato paste and milk and add to egg mixture. Whisk well. Add onions and garlic to egg mixture.
Thoroughly grease casserole dish. Remove potatoes from water and dry with a paper towel. Add raw potatoes and pour in *melted butter. If using defrosted French Fries or Hash Browns, skip the melted butter.
Pour in egg mixture and any add ins and top with cheese (if using).
Add water to Pressure Cooker cooking pot and place a Trivet. Place uncovered casserole dish on Trivet.
Lock on lid and close Pressure Valve. Cook on High Pressure for 15-20 minutes.
When Beep sounds, allow a 10 minute Natural Pressure Release and then release the rest of the pressure.
Top with grated cheese (if using) and place Lid on top of Pressure Cooker and allow cheese to melt.
Some people add extra goodies or don't beat the eggs until fluffy, so if the Frittata is still soft when you open the Pressure Cooker, cook for another 5 minutes.Others like a harder Frittata, so adjust your time accordingly.Adding Cheese is not traditional to a Spanish or Cuban Frittata. My husband loves Cheese, so we sometimes add it in.