In a small pot, set over medium-low heat, warm the milk, butter a honey, until butter is melted, being sure it's not too hot (it should be lukewarm) or else yeast won't rise. If it does get a bit too hot, simply let it stand at room temperature until it cools down.
In a small bowl, add the egg and egg yolks and beat until combined.
In the bowl of a stand-up mixer (with the hook attachment), add the flour, instant yeast and salt. Gently mix all ingredients before adding the liquid mixture.
Pour the liquid mixture into the dry ingredient.
Next, add the egg one at a time. Then add in the egg yolk to the flour mixture and knead with machine on medium speed for about 5-7 minutes, until smooth and elastic.
The dough will be quite wet and that's ok! Rub a medium bowl with about a teaspoon of (I used olive oil), and transfer the dough to the bowl. Cover with a clean kitchen towel allow to rise for 30-40 minutes. Alternatively, cover the bowl with a lid or plastic wrap allow to rise in the fridge for 12 to 24 hours.
Assemble The Rolls:
Divide and roll the dough into balls, stretching the dough and pinching it under the ball of dough to make sure it has a smooth top.
Transfer them to the buttered pan and allow them to rise for about 1 to 1½ hours. They should have doubled in size and should be puffy and supple.
*Note: if you let the dough rise in the fridge overnight, you can assemble them straight from the fridge but they may need to rise for a bit longer (since the dough will be quite cold). It may take about 1 1/2 hours for them to rise after assembled!
Preheat the oven to 180°C. Brush the tops of the rolls with egg wash and transfer to the oven to bake until golden brown, about 20 minutes.
Honey Butter:
In a small saucepan, melt the butter and add the honey. Mix together until smooth.
When the buns come out of the oven, immediately brush the tops with the honey butter mixture and sprinkle with flakey sea salt.