Add rice and 1 1/4 cups water to the instant pot. Lock lid; set valve to sealing. Program for manual-high and 22 minutes. Allow for natural pressure release. Open lid and press sauté, then adjust to “less”. Stir in one cup milk, cinnamon, and salt. Heat, stirring constantly, until rice mixture is thickened and creamy. Stir in egg and remaining milk. Heat and stir until thick, about 5 minutes. Stir in butter, raisins, vanilla, and nutmeg. Garnish with cinnamon sticks, if desired.
(Note: if your IP seems too hot, press cancel and allow it to cool a little, then turn it back to saute- less. Repeat this procedure as needed.)