Add egg yolks and whisk until smooth and pale yellow in color

Heat milk with lemon zest in a saucepan until steaming but not boiling

Slowly pour warm milk into the egg mixture while whisking continuously

Return mixture to the saucepan and cook while stirring until thick and creamy

Remove from heat and stir in butter until fully melted and glossy

Strain the cream into a clean bowl and cover the surface to prevent skin forming

Chill the lemon cream until completely cold and set

Stir in a portion of lemon juice to brighten the flavor

Toss blueberries with sugar and lightly mash some to release juices

Combine cake cubes with simple syrup and remaining lemon juice until lightly soaked

Layer half of the cake in a glass dish, pressing gently for an even base

Spread half of the lemon cream over the cake in a smooth layer

Spoon half of the blueberries and juices evenly over the cream

Repeat layers with remaining cake, cream, and blueberries

Chill before serving until the layers are set and flavors meld together