In a large bowl, combine all-purpose flour, instant yeast, sugar, and salt. Gradually mix in the milk and eggs, then knead by hand until no dry flour remains, about 5–7 minutes.

To ensure your brioche dough is well developed, stretch a small piece between your fingers. If it forms a thin, translucent membrane without tearing, you're good to go; if not, continue kneading for a couple more minutes.

Cover the prepared brioche dough with plastic wrap and refrigerate for at least 2 hours, or overnight if desired.

In a saucepan, whisk together custard powder, sugar, and milk over medium heat. Continuously stir until thickened, about 5–7 minutes.

In another small saucepan, combine chopped rhubarb, a splash of water, and sugar. Cook over medium heat until soft, around 8–10 minutes.

On a lightly floured surface, roll out the chilled brioche dough into a rectangle about ½ inch thick. Spread a layer of cooled custard across the dough, followed by dollops of rhubarb compote. Roll tightly and cut into pieces, placing them into muffin cups.

Cover the assembled buns with a kitchen towel and let them rise in a warm place for about 30–45 minutes. Preheat the oven to 350°F (175°C). Bake for 20–25 minutes, or until golden.