In a large bowl, combine flour, sugar, yeast, salt, and cardamom. Add the eggs and milk. Mix until a dough forms.
Knead by hand for around 20 minutes, or in a stand mixer fitted with a dough-hook for about 10 minutes, until smooth, elastic, and just tacky. The dough should stretch into a thin membrane without tearing.
Add the butter gradually. By hand, work it in 3–4 additions, smearing and kneading until fully incorporated. In a mixer, add small pieces one by one. The dough will look split at first – keep going until smooth again.
Place in a large bowl, cover, and chill. Either proof 1 hour at room temperature, then refrigerate for 2 hours, or refrigerate straight away for at least 8 hours (and up to 24 hours).
The next day, line two trays with baking paper. Mix the filling ingredients until smooth.
On a lightly floured bench, roll the dough to a 30 × 60 cm rectangle, about 5–6 mm thick. Spread with cinnamon butter. Fold the dough into thirds (like a letter), giving you a rectangle about 30 × 20 cm.
Cut into 2 cm strips. Twist and tie each into a knot. Place on trays. Cover loosely and proof until doubled – around 2 hours.
Preheat oven to 200°C / fan 180°C. Brush the buns with egg wash, sprinkle with pearl sugar, and bake 12–16 minutes, until golden.
For extra shine, brush with hot syrup as soon as they come out of the oven. Cool slightly on a wire rack.