Mix all dough ingredients until combined, then let rest for 30 minutes
Knead 10 to 15 minutes until smooth, elastic, and slightly shiny
Cover and refrigerate 8 to 12 hours
Divide into 60 g pieces, shape into balls, and let rise 1½ to 2 hours until doubled
Brush with egg wash and bake at 180°C (350°F) for 12 to 15 minutes until golden. Cool completely
Heat milk, cream, and vanilla. Whisk sugar, yolks, and cornstarch, then cook with the hot milk until thick. Mix in butter and gelatin, then chill
Heat cream with vanilla. Caramelize sugar, carefully add cream, cook briefly, then mix in butter and salt. Let cool
Melt chocolate with coconut oil until smooth
Fill brioche with pastry cream, add caramel, dip in chocolate, and finish with flaky salt if desired
