Bialy Babka

Ingredients

• unsalted butter — divided85 g
• whole milk90 ml
• instant yeast1.75 tsp
• granulated sugar15 g
• fine sea salt — 1 ½ tsp; divided9 g
• large eggs — 1 whole and 1 yolk only2 ea
• all-purpose flour295 g
• yellow onions — diced680 g
• poppy seeds — divided9 g

Method

1. Make the dough: melt 55 g of the butter. In the bowl of a stand mixer, whisk together the melted butter, milk, yeast, sugar, 3/4 teaspoon salt, the egg and the yolk. Add the flour and knead with the dough hook on low for 5 to 7 minutes, until stretchy but soft. Transfer to an oiled bowl, cover tightly and leave in a warm spot for 1 1/2 to 2 hours, until about doubled. (In a cold kitchen, heat the oven to 200°F (95°C) for a few minutes, turn it off and rise the dough in there.)
2. While the dough rises, cook the onions: melt the remaining 30 g butter in a large sauté pan over medium heat. Add the onions, toss to coat, cover and reduce to medium-low. Let them steep for 12 to 15 minutes, stirring once or twice.
3. Uncover, raise the heat slightly and stir in the remaining 3/4 teaspoon salt. Cook, stirring every 5 minutes, for another 20 to 30 minutes, until golden brown, very tender and sweet. Raise the heat to medium-high and cook until a little dark at the edges, about 5 minutes more. Spread out on a plate to cool.
4. Assemble: on a well-floured counter, roll the dough out to about 30 cm wide and as long as you can roll it thin, likely 25 to 35 cm. Spread the onions over in an even layer and sprinkle with 2 teaspoons poppy seeds. Roll up into a tight coil and chill on a parchment-lined tray in the freezer for 5 to 10 minutes.
5. Butter a standard loaf pan and line the bottom and two sides with a parchment sling.
6. Cut the chilled log lengthwise into two long strips and lay them side by side, cut sides up. Lift one over the other to form a twist, keeping the cut sides facing up, and transfer to the loaf pan. Cover and let rise another 45 minutes at room temperature.
7. Heat the oven to 350°F (175°C). Sprinkle the babka with a couple of extra pinches of poppy seeds and bake for 40 to 45 minutes, until a skewer in the centre doesn't hit sticky dough or the internal temperature is 185°F (85°C). Cover with foil for the last few minutes if the onions brown too much.
8. Cool in the pan as long as you can stand, then cut into thick slices with a serrated knife. Leftovers keep at room temperature, wrapped in foil, for a few days; toast slices gently to rewarm.