Preheat a convection oven to 175°C (350°F).

Apply 15g of softened butter to the interior surfaces of a 23x33cm (9x13 inch) ceramic baking dish.

Bisect the 20 pre-cooked pancakes into semi-circles using a chef's knife.

Align the pancake halves cut-side down in the baking dish in three parallel rows, ensuring a slight overlap to create a shingled texture.

In a stainless steel mixing bowl, combine the 6 eggs, 540ml half-and-half, 100g brown sugar, vanilla extract, cinnamon, and salt.

Whisk the mixture vigorously for 60 seconds until the custard is fully emulsified and the sugar is dissolved.

Pour the custard slowly over the arranged pancakes, ensuring even distribution and saturation of the pancake surfaces.

Intersperse the 200g of fresh blueberries into the interstitial spaces between the pancake layers.

Allow the assembly to rest for 10 minutes at room temperature to facilitate custard absorption.

Bake on the center rack for 45 to 50 minutes until the custard is set and the internal temperature reaches 74°C (165°F).

Remove from the thermal source and allow the structure to stabilize for 300 seconds before portioning.