Step 1

Make the pastry cream: Sift together the sugar, cornstarch and salt in a medium bowl. Whisk in the egg yolks until the sugar dissolves and the yolks turn pale yellow. Set aside.

Step 2

In a blender, combine the milk, half-and-half, and mashed banana. Blend until smooth. Pour into a medium heavy-bottomed saucepan and add the vanilla bean, if using. Cook over medium heat until bubbles begin to form around the edges.

Step 3

Set a fine-mesh sieve over the bowl of egg yolks. Ladle in the hot milk a little at a time, through the sieve, and whisk together. When the bottom of the bowl feels warm, whisk in the remaining milk.

Step 4

Pour the mixture back into the saucepan and bring to a full boil, whisking constantly (scraping the bottom and sides of the saucepan), until the pastry cream thickens and no longer tastes chalky.

Step 5

Strain the pastry cream through a fine-mesh sieve into a large heatproof bowl, pushing it through with a rubber spatula. Add the vanilla extract, if using, and the butter; stir until smooth. Cover with plastic wrap and press it directly onto the surface. Refrigerate until cold, about 2 hours.

Step 6

Meanwhile, make the meringue: Put the egg whites, sugar and salt in the bowl of a stand mixer or other large heatproof bowl. Place over a large saucepan of simmering water (do not let the bowl touch the water) and whisk constantly until the sugar dissolves and an instant-read or candy thermometer registers 165 degrees F. Beat the egg whites with an electric mixer on medium-high speed until shiny, stiff peaks form, about 5 minutes. Add the vinegar, vanilla and banana extracts and whisk until the bowl no longer feels warm, scraping down the sides of the bowl as needed.

Step 7

Finish the pastry cream: Beat the heavy cream with an electric mixer on medium-high speed until soft peaks form, about 30 seconds. Whisk one-third of the whipped cream into the chilled pastry cream to loosen it, then gently fold in the remaining whipped cream until incorporated. Cut the 2 bananas into 1/2-inch-wide chunks and gently fold into the pastry cream.

Step 8

Break 4 of the shortbread cookies into bite-size pieces and spread in the bottom of a trifle bowl. Top with half of the banana pastry cream. Break another 4 cookies and scatter over the pastry cream. Top with the remaining pastry cream. Break another 4 cookies and scatter over the pastry cream. Top with as much of the meringue as desired and swirl decoratively into peaks. Torch the meringue, if desired. Cut the banana on the bias into 1/2-inch-thick slices. Garnish the top of the meringue, alternating the banana slices with the remaining shortbread cookies. Alternatively, break 1 shortbread cookie into the bottom of each of 8 ramekins. Divide the pastry cream among the ramekins, then top with the meringue. Garnish with cookies and banana slices. Enjoy!

Step 9

Whisk the flour and salt in a medium bowl. Beat the butter and sugar in a stand mixer fitted with the paddle attachment on medium speed until creamy. Beat in the vanilla until incorporated.

Step 10

Reduce the speed to low and gradually add flour mixture. Beat, scraping the bowl occasionally, until the dough comes together in large clumps.

Step 11

Transfer the dough to a gallon-size resealable plastic freezer bag and press into a 1-inch thick, 9 by 5-inch rectangle. The bag is 9 inches wide, so you're pressing the dough to the edges. Refrigerate until firm, at least 2 hours and up to 2 days.

Step 12

When ready to bake, preheat the oven to 350 degrees F. Line baking sheets with parchment paper.

Step 13

Cut the dough into thirds to form rectangular logs that are 3 inches wide. Cut each log into 1/4-inch-thick slices. Place the slices on the prepared baking sheets, spacing them 1/2 inch apart.

Step 14

Bake one sheet at a time until the edges are browned and the tops are golden, 14 to 18 minutes. Let cool completely on the sheets on wire racks. The shortbread keeps at room temperature in an airtight container for up to 2 weeks.