01 - Preheat oven to 400°F. Whisk flour, sugar, baking powder, and salt in a large bowl. Cut cold butter into mixture until coarse crumbs form. Whisk milk and egg in separate bowl, then incorporate into flour mixture until just combined. Drop 8 large spoonfuls onto parchment-lined baking sheet. Bake 15–18 minutes until golden brown. Cool completely, then break into bite-sized pieces.
02 - Heat milk in saucepan until just simmering. Whisk sugar, egg yolks, cornstarch, and salt until smooth. Gradually temper hot milk into yolk mixture while whisking. Return to saucepan and cook over medium heat, whisking constantly, for 3–5 minutes until thickened. Remove from heat, stir in vanilla. Transfer to bowl, press plastic wrap directly onto surface, and refrigerate until completely cold.
03 - Combine sliced strawberries with sugar and lemon juice in bowl. Let stand at room temperature for minimum 20 minutes, allowing natural juices to release and create syrup.
04 - Whip heavy cream, powdered sugar, and vanilla extract in chilled bowl until soft peaks form. Keep refrigerated until assembly.
05 - Layer half the shortcake pieces in bottom of trifle dish. Spread half the custard evenly over cake. Distribute half the macerated strawberries with their juices. Top with half the whipped cream. Repeat layering sequence with remaining ingredients. Garnish top with additional strawberry slices and whipped cream dollop if desired.
06 - Refrigerate assembled trifle for at least 1 hour to allow flavors to meld and textures to set properly. Serve chilled.