Make the Custard:

1. Heat the milk: In a 3-quart saucier, combine milk and vanilla bean. Heat over medium until milk is steaming, then remove from heat and let steep for 30 minutes. For a stronger vanilla flavor, refrigerate for up to 24 hours.

2. Mix sugar, cornstarch, and eggs: In a medium bowl, whisk sugar and cornstarch, then add eggs and mix until smooth.

3. Temper the egg mixture: Reheat the milk until steaming again. Gradually whisk ½ cup of hot milk into the egg mixture, then slowly add the rest of the milk.

4. Cook the custard: Return to heat and whisk constantly for about 3 minutes until thickened. Continue for 2 more minutes, then transfer to a 7×11-inch baking dish. Press plastic wrap directly onto the surface and refrigerate for 1 hour.

Finish the Buttercream:

1. Cream butter and cream cheese: Beat softened butter and cream cheese in a stand mixer for 5 minutes until light and fluffy.

2. Add cooled custard: Whisk cooled custard until smooth and gradually add it to the butter mixture, beating well after each addition.

3. Whip the frosting: Switch to the whisk attachment and whip the frosting on medium speed. Gradually add lemon juice and continue whipping until smooth.

Use or Store:

• Use immediately: Frost your favorite cake or cupcakes.

• Store: Refrigerate in an airtight container for up to 3 weeks or freeze for up to 3 months. When ready to use, thaw in the fridge and rewhip.