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To make the sponge: Combine the milk, yeast, and sugar in the bowl of your stand mixer. We don't recommend kneading this dough by hand; it's too sticky.
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When the yeast is dissolved, whisk in the eggs. Stir in 1 cup of the flour and sprinkle the remaining 1/2 cup over the top. Set aside to rise until there are cracks in the layer of flour on top, about 30 minutes.
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To make the dough: Add the flour, sugar, salt, eggs, egg yolk, and tahini to the sponge. Mix until dough forms, using the mixer's dough hook attachment.
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Increase the speed to medium and mix until the dough begins to gather itself around the hook, about 8 to 10 minutes. When ready, the dough should bounce back if you poke it with your finger; if it's still sticky, add 2 more tablespoons of flour (but no more) and knead for 2 more minutes. It's important that the dough is developed before adding the butter.
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Scrape the sides and bottom of the bowl and mix again on high speed for 1 minute. Reduce the speed to medium, add half of the butter, and continue mixing until the butter is incorporated.
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Add the remaining butter and continue mixing until the dough is silky smooth, 10 to 15 minutes. Increase the speed to medium-high and beat until the dough pulls away from the side of the bowl, about 1 minute.
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Lightly flour a bowl or storage container. Transfer the dough to the container and press it into a flat rectangle. Fold the edges in to meet in the middle, then flip the dough over and press into a rectangle once more. Cover and refrigerate for at least 6 hours or as long as overnight.
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To shape the rolls: Butter a 9" or 10" springform pan and set aside. Divide the dough into 12 pieces and roll into balls. Arrange the balls in a single layer in the prepared pan.
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Cover with plastic and let rise at room temperature until almost doubled in size, 1 1/2 to 2 hours.
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To bake: Toward the end of the rise time, preheat the oven to 350°F. When the rolls have properly risen, they'll look puffy and a slight dent will remain when gently pressed. Brush the tops with the beaten egg white and sprinkle with sesame seeds.
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Bake for 30 to 35 minutes, until golden brown and the center reads 190°F when measured with a digital thermometer. Remove from the oven and place on a rack. After 5 minutes, remove the side of the pan to allow the rolls to finish cooling.
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Store leftover rolls, well wrapped, at room temperature for up to three days; freeze for longer storage.