Spray 6 inch to 7 inch soufflé dish or round baking dish that fits inside Instant Pot with nonstick cooking spray.
Combine bread cubes and raisins in prepared dish; toss to distribute raisins evenly.
Whisk milk, eggs, egg yolk, sugar, cinnamon and nutmeg in medium bowl until well blended. Pour over bread mixture; press bread down into liquid. Cover dish tightly with foil; let stand 15 minutes.
Pour 1 1/2 cups of water into Instant Pot. Place soufflé dish on rack; lower into pot using handles of rack.
Secure lid and move pressure release valve to Sealing position. Press Manual; cook at high pressure 35 minutes. Meanwhile, prepare Vanilla Rum Sauce, if desired.
When cooking is complete, use natural release for 10 minutes, then release remaining pressure.
Use handles of rack to remove dish from pot. Remove foil; serve bread pudding warm with sauce.
To Make the Sauce:
Beat egg yolks and sugar in small bowl until light and fluffy.
Heat whipping cream to a simmer in medium saucepan over medium-high heat.
Slowly add egg yolk mixture, whisking constantly 2 minutes. Remove from heat; strain into medium bowl.
Stir in 2 tablespoons dark rum or brandy and 1⁄4 teaspoon vanilla. Serve warm or at room temperature. Makes about 1 1⁄4 cups.