For the pudding:
1/2 cup granulated sugar
1/4 cup cornstarch
1/2 teaspoon fine salt
2 large eggs
1 large egg yolk
2 cups whole milk
1/2 cup heavy cream
2 teaspoons vanilla extract
3 slightly underripe bananas
1 tablespoon freshly squeezed lemon juice
1 (9-ounce) package chocolate wafer cookies
1 cup cold heavy cream
2 tablespoons granulated sugar
8 maraschino cherries
Place the sugar, cornstarch, and salt in a medium saucepan. Whisk together, breaking up any clumps in the sugar or starch. Add the eggs and egg yolk to the sugar mixture and whisk until completely smooth. Whisk in the milk and cream.
Heat the mixture over medium heat, stirring constantly, until the mixture thickens and bubbles around the edges, 8 to 10 minutes. Remove the pan from the heat and whisk in the vanilla extract.
Pour the custard into a 9x13-inch baking dish and spread into an even layer. Place a layer of plastic wrap directly onto the custard and chill for at least 2 hours or up to 3 days before building the trifle.
Peel the bananas and slice into 1/4-inch-thick rounds. Place in a medium bowl, add the lemon juice, and toss to combine.
Fill 8 custard cups or ramekins each with 1/4 cup pudding. Top each with 2 to 3 chocolate wafer cookies and a few slices of banana. Repeat layering until all the pudding has been used. Refrigerate while whipping the cream.
Whip the cream in a stand mixer or with a hand mixer on medium speed until foamy. While whisking, add the sugar gradually, and continue whipping to stiff peaks.
Top the banana puddings with the whipped cream, some sprinkles, and a cherry before serving.