Step 1

To make the ube cookie dough : In a large bowl or the bowl of a stand mixer, beat (“cream”) together the butter and sugar until pale in color and fluffy, 3 to 4 minutes. Scrape the sides of the bowl as needed.

Step 2

, To the butter/sugar mixture, add the egg, jam, and extract and mix until incorporated, 1 to 2 minutes. Add the flour, baking powder, and salt and mix until just combined, less than 30 seconds. Cover and refrigerate for at least 1 hour or overnight.

Step 3

, To make the mochi filling : In a medium microwave-safe bowl, whisk the rice flour, confectioners’ sugar, cornstarch, and water until no lumps remain. Cover loosely, microwave on high power for 1 minute, then use a spatula to mix until evenly combined. Microwave for another minute and mix again. If there are any wet parts remaining, microwave for an additional minute at 50% power. The mochi is ready when it's slightly translucent, cohesive, and evenly cooked.

Step 4

, Add the butter and mix thoroughly to incorporate.

Step 5

, Cover and let cool until the mochi is no longer too hot to touch, about 8 to 10 minutes.

Step 6

, Working with damp hands, stretch and fold the mochi until it's smooth, elastic, and homogenous, about 15 seconds. It’ll still be sticky. Cover and set aside until ready to bake.

Step 7

, Preheat the oven to 350°F and place a rack in the center. Line a baking sheet with parchment.

Step 8

, To assemble the ube cookies : Working with damp hands, pull off 12 tablespoon-sized pieces of mochi (about 10g each) and place them on a nonstick surface, like a silicone mat or piece of plastic wrap, as you work. If the mochi is too sticky to handle, rub a bit of neutral oil on your palms. (You will have a bit of leftover mochi; see "tips" below for details on delicious ways to use it up.)

Step 9

, Scoop 1 1/2 tablespoons (about 35g) of cookie dough onto the prepared sheet; a heaping tablespoon cookie scoop works well here. Shape the scooped dough into balls. Pat and press one ball of cookie dough into a 3" round between your palms, lightly flouring your hands as needed to prevent sticking. Place a mochi ball in the center of the disk, wrap the cookie dough around it, close the seams, and re-roll into a smooth, firm ball. Distribute the shaped cookies evenly on the prepared baking sheet, leaving about 2" of space between them.

Step 10

, Place the granulated sugar and confectioners’ sugar each in their own a shallow bowl. Working with one dough ball at a time, toss it in the granulated sugar, coat thoroughly, then transfer it to the confectioners’ sugar and turn until well-coated. (Coating in granulated sugar first prevents the coating from dissolving into the dough.) Place on the prepared baking sheet and repeat until you’ve made a total of 12 dough balls.

Step 11

, Bake the cookies for about 16 to 18 minutes, until the edges have set. The cookie centers should be soft but not wet or shiny.

Step 12

, Cool on the baking sheet for a few minutes, then transfer to a wire rack to cool completely.

Step 13

, Storage instructions : Store ube cookies loosely wrapped at room temperature for up to 3 days (the mochi will a get bit firmer over time). Freeze mochi-stuffed cookie dough balls after step 6 (assembly) and before step 7 (coating in sugar). When ready to bake, let dough balls sit at room temperature for 5 to 10 minutes before coating in sugar (this will make the sugar adhere more readily). Bake as directed, adding 4 to 5 minutes to the bake time if necessary. Baked cookies can also be frozen. Thaw in the refrigerator overnight before enjoying.