For the dough: In the bowl of a stand mixer fitted with the whisk attachment, whisk the egg yolks, whole egg, sugar, butter, and buttermilk on medium speed. for 1 minute. Add 2 cups (295 grams) of the flour along with the yeast and salt and whisk for another minute until moistened and combined, scraping the bowl with a rubber spatula halfway through. Remove the whisk attachment and replace with a dough hook. Add all (197 grams) but 3/4 cup (100 grams) of the remaining flour and knead on low speed for 5 minutes. Check the consistency of the dough and add more flour if necessary. The dough should feel soft and moist but not sticky. Knead on low speed until the dough clears the sides of the bowl, about 5 minutes more. Turn the dough out onto a lightly floured work surface and knead by hand about 30 seconds. Lightly oil a large bowl. Transfer the dough to the bowl, lightly oil the top of the dough, cover, and let double in volume, 2 to 2 1/2 hours.
For the topping: Place a 2-quart saucepan over medium heat. Combine the 2 sticks of unsalted butter, brown sugar, rosemary, and raisins. Cook, stirring occasionally, until the butter is melted and the sugar is dissolved, about 3 minutes. Pour half of the topping into the bottom of 2 bundt pans and set aside. Cover and store the other half of the topping in the refrigerator until the next morning.
For the coating: Place the melted butter and rosemary in a shallow bowl and stir to combine.
Once the dough has risen, turn out onto a lightly floured surface. Shape the dough into an 18-inch long cylinder and portion into 1-ounce pieces with a bench scraper then roll each piece into a ball — you should have approximately 32 balls. Roll the balls in the coating and divide evenly between the 2 bundt pans. Cover with plastic wrap and place in the refrigerator overnight or up to 16 hours.
Remove the bread from the refrigerator and place in an oven that is turned off. Fill a shallow pan 2/3 full of boiling water and set on the rack below the bread. Close the oven and let the bread rise until slightly puffy looking, 20 to 30 minutes. Once the bread has risen, remove it and the shallow pan of water from the oven.
Heat oven to 350ºF.
Once the oven is ready, place the bread on the middle rack and bake until slightly golden on top or until the internal temperature reaches 190ºF on an instant-read thermometer, 25 to 30 minutes
Place the remaining topping in a small saucepan and set over medium heat. Reheat until the mixture is pourable, approximately 5 minutes. Fifteen minutes into baking, pour the remaining topping over the bread, and finish cooking. Cool on a wire rack for 5 minutes, then invert onto a platter or cutting board. Serve immediately.