Ube Buns

Combine 1 cup water and coconut milk in a medium-size microwavable bowl. Microwave on high until warmed to about 110°F, 30 to 40 seconds. Stir in yeast; let stand until foamy, about 5 minutes. Stir in butter and ube extract. Set aside.

Stir together all-purpose flour, purple sweet potato flour, sugar, baking powder, and salt in bowl of a stand mixer fitted with the dough hook. With mixer running on low speed, gradually stream yeast mixture into flour mixture. Beat on low speed until all dry ingredients are incorporated, about 1 minute. Increase mixer speed to medium, and beat until dough is smooth, elastic, and sticky, about 5 minutes. If dough feels too sticky, add up to 2 tablespoons additional flour, starting with 1 tablespoon, and beat until incorporated.

Using lightly greased (with cooking spray) hands, shape dough into a ball, and transfer to a lightly greased large bowl. Cover tightly with plastic wrap, and let proof at room temperature until doubled in volume, at least 40 minutes or up to 1 hour.

Meanwhile, cut 8 (4-inch) parchment paper squares. Arrange parchment paper squares evenly spaced on each tray of a 12-inch double-tier bamboo steamer, and set aside.

Turn dough out onto a lightly greased (with cooking spray) work surface, and divide evenly into 8 pieces (about 3 3/4 ounces each). Using a lightly greased hand, place 1 dough ball on an ungreased work surface. Make a claw shape with your hand, and, using the tension of the surface, shape dough into a taut ball. Place ball on 1 prepared parchment square in bamboo steamer. Repeat process with remaining dough pieces, regreasing hand as needed. 

Stack bamboo trays, and place lid on steamer. Let dough proof at room temperature until volume has increased by about 1 1/2 times, about 45 minutes. After about 30 minutes of proofing time, fill a wok or large skillet with water to a depth of 2 inches, and bring to a boil over medium-high.

Once buns have proofed, place steamer over boiling water; crack lid slightly to form a 1/4-inch gap for steam to release. Cook over medium-high, without opening lid, 25 minutes. Remove from heat; let buns cool, without opening lid, 5 minutes.

Remove steamer from wok; remove lid, and unstack trays. Let buns cool slightly, about 15 minutes, or let cool completely, about 30 minutes. Split buns in half horizontally for burgers. Buns may be stored in an airtight container or ziplock plastic bag up to 1 day or in freezer up to 1 month.