Preheat oven to 375 degrees. Lightly dust a clean work surface with flour, and roll out pate brisee to a 1/8-inch thickness. Fit into a 9-inch deep-dish pie plate. Trim pastry using scissors or a sharp paring knife. Crimp or decorate edges of pastry if desired. Chill for 30 minutes.
Carefully line pastry with parchment paper, pressing it into corners and edges, and weight with beans, rice, or aluminum or ceramic weights. Bake until pastry begins to color around edges, about 15 minutes. Remove paper and weights, and continue to bake just until pastry dries out and turns golden brown, 10 to 15 minutes more.
Cool completely on a wire rack. The baked shell can be stored in airtight containers or well wrapped in plastic in the freezer for up to 1 month.
Prepare an ice-water bath; set aside. Make the custard: In a medium bowl, whisk together egg yolks, granulated sugar, cornstarch, and salt. In a medium saucepan, bring milk just to a boil. Remove from heat, and whisk about 1/2 cup of hot milk into yolk mixture. Whisk yolk mixture into saucepan of hot milk. Place over medium-high heat, and bring to a gentle boil, whisking constantly. Continue to cook, whisking constantly, until thickened, about 1 minute. Remove from heat, and whisk in butter, one piece at a time, until melted. Add 1 teaspoon vanilla, and whisk until smooth. Immediately strain through a fine-mesh sieve into a medium bowl. Place bowl of custard in ice bath to cool, stirring occasionally.
Peel bananas, and slice 1/4 inch thick. Add lemon juice, and toss gently to coat. Arrange in an even layer in bottom of baked piecrust. Scrape cooled custard over bananas, and smooth top with a spatula. Refrigerate for at least 2 hours or up to overnight.
In the bowl of an electric mixer fitted with the whisk attachment, beat cream on medium-low speed for 30 seconds. Increase speed to medium-high, and add confectioners' sugar and remaining 1/2 teaspoon vanilla. Beat until soft peaks form. Transfer to a pastry bag fitted with a large star tip (Ateco No. 32). Pipe cream over custard in large rosettes, covering it completely. Serve immediately.