In a medium bowl, whisk the egg yolks and butter. Add the water and whisk until well combined. Set aside.
Using a stand mixer with paddle attachment, whisk the flour with the sugar, yeast, and salt. Add the egg yolk mixture and mix for about 1 minute, or until well combined.
Change to the dough hook and knead for about 10 minutes, on medium speed. The dough should be soft (add a little more flour if the dough is too sticky).
Preheat the oven to 350°F (176°C).
Transfer the dough to a clean, oiled bowl. Cover with a kitchen towel and let rise in a warm place, or in a 100°F (37℃) warm oven, for about 60-70 minutes or until spongy.
Turn out the dough onto a flat surface dusted with flour. Knead with hands and cut into 6 equal pieces. Cover with a towel and rest for about 15 minutes.
Line a baking sheet with parchment paper. Roll each dough into a log (10″ (25cm) long). Fold the log into a knot (watch the video on my Garlic Parmesan Dinner Roll recipe). Transfer the knots to the baking sheet and brush with the beaten egg white. Let them rise for about 30 minutes, or until puffy. Repeat the egg wash again and sprinkle with salt.
Bake for about 20 minutes or until the Challah knots are golden brown and shiny. Remove from the oven and serve warm.