I was going to add cinnamon to the purple sweet potato but realized that I wanted this bread for sandwiches so the cinnamon wouldn’t be a good idea. However, if this bread was for toast, adding some cinnamon to the purple sweet potato would have been delicious. To make this bread, you’ll need to prepare some mashed purple sweet potato. I did this a while back, then portioned and froze the portions in ziplock bags. Once defrosted I blend the mash with a combination of sugar and flour. I have found that when there is a sweet filling in my breads that the sugar draws out water from the dough. This ends up causing problems with separation between the filling and bread and also collapsing or a pinched waist in the baked bread. To counter this, I have found that adding some flour to the filling helps absorb the water coming out of the dough, so far this has worked every time.
For one 9x4x4” Pullman pan loaf.
Purple Sweet Potato Filling
100 g mashed sweet potato
12 g granulated sugar
12 g flour
Mix together and set aside.
Egg/milk wash: 1 yolk and 1 tbsp milk, beaten
Instructions
Levain
Mix the levain ingredients in a jar or pyrex container with space for at least 300% growth.
Press down with your knuckles or silicone spatula to create a uniform surface and to push out air.
At a temperature of 76-78ºF, it typically takes up to 10-12 hours for this sweet stiff levain to be at peak. For my starter I typically see 3-3.5 times increase in size at peak. The levain will smell sweet with only a mild tang.
Tangzhong
In a sauce pan set on medium heat, stir the milk and whole wheat flour until blended. Then cook for several minutes until well thickened, stirring regularly with a spoon or heat-resistant spatula. Let cool in the pan or, for faster results, in a new bowl. Theoretically it should reach 65ºC (149ºF) but I don’t find I need to measure the temperature as the tangzhong gelatinizes at this temperature. You can prepare this the night before and refrigerate it, ensure that it is covered to prevent it from drying out.
If you plan on using a stand mixer to mix this dough, set up a Bain Marie and use your stand mixer’s bowl to prepare the tangzhong.
Dough
In the bowl of a stand mixer, add the milk (consider holding back 10 g of milk and adding later if this is the first time you’re making this), egg, tangzhong, salt, sugar and levain. Mix and then break up the levain into many smaller pieces. Next add the flours. I like to use my spatula to mix until there aren’t many dry areas. Allow the flour to hydrate (fermentolyse) for 20-30 minutes. Mix on low speed and then medium speed until moderate gluten development this may take 5-10 mins. You may want to scrape the sides of the bowl during the first 5 minutes of mixing. Next add room temperature butter one pat at a time. The dough may come apart, be patient, continue to mix until it comes together before adding in more butter. You will want to check gluten development by windowpane during this time and stop mixing when you get a good windowpane. You should be able to pull a good windowpane.
On the counter, shape the dough into a tight ball, cover in the bowl and ferment for 2 - 4 hours at 82ºF. There should be some rise visible at this stage.
Butter a large baking pan. Punch the dough down and then divide into 2 equal portions. Form each into tight boules. Stretch and then roll each piece of dough into a large rectangle, approximately equal sizes. Spread the prepared purple sweet potato filling evenly over one of of the rectangles of dough leaving about 1cm at the edge of dough without mashed potato. Place the other rectangle of dough onto the other sandwiching the sweet potato between them. Using a rolling pin, roll the dough out a bit more aiming for more than 12” in length and just under 9” in width.
Using a ruler and pizza cutter, cut the dough into evenly wide strips about 1.5-2 cm wide along the length of the dough but leaving about 2-4 cm of dough uncut at the end furthest away from you. When all the strips are cut, twist the strips in alternating directions, clockwise and then counter clockwise. Once all the strips are twisted, roll the whole thing into a log starting furthest away from you getting a nice tight roll at the start. Transfer the dough into your prepared pullman pan with the seam side down.
Place in the buttered baking pan seem side down. Cover them and allow them to fully proof until the top of the dough reaches within 1 cm of the rim of the pan.
When there is about 30 mins left of proofing time, prepare your egg and milk wash and then brush the top of the loaf.
About 30 mins prior to end of final proof preheat the oven to 350°F.
Immediately prior to baking brush the dough again with the egg and milk mixture.
Bake the bread for 50 minutes or until the internal temperature is at least 190F. Cover if your loaf gets brown early in the baking process.
Remove the bread from the pan and return to the oven baking directly on the rack if the sides of the loaf aren’t yet crisp baking for another 5-10 mins. Cool on a rack, enjoy.
