3â„4 cup nonhydrogenated shortening, or 12 tablespoons (11â„ 2 sticks) unsalted butter at room temperature, or a combination of shortening and butter
11â„ 2 cups dark brown or muscovado sugar, packed
3 tablespoons whole milk or soy milk
2 tablespoons canola oil
1 cup creamy peanut butter
1 teaspoon vanilla extract
3â„4 cup strawberry, or your favorite, preserves
Position oven racks in the center and top third of the oven and preheat to 350Â°F. Line two baking sheets with parchment paper or silicone baking mats.
Mix together the whole wheat flour, cornstarch, baking powder, baking soda, and salt. Using an electric mixer at high speed, beat the shortening in a large bowl until smooth. Gradually beat in the brown sugar, then the milk and oil, beating well after the addition of each. Add the peanut butter and vanilla and beat, scraping the sides of the bowl often, until the mixture is paler, about 2 minutes. Reduce the mixer speed to low. Add the flour mixture and mix just until combined.
Using a level tablespoon of dough for each cookie, roll the dough into balls. Place 1 inch apart on the baking sheets. Using your thumb, make a deep indentation in the center of each ball. If the preserves have large chunks of fruit, whirl in a food processor fitted with the metal chopping blade until the fruit is very finely chopped. Transfer the preserves to a small zippered plastic bag and squeeze the preserves into one lower corner of the bag. Snip off the tip of the corner with scissors. Pipe the preserves into the indentations in the cookies, about 1â„2 teaspoon per cookie.
Bake until the cookies are lightly browned around the edges, switching the positions of the sheets from top to bottom and front to back halfway through baking, 12 to 15 minutes. Cool on the sheets for a few minutes, then carefully transfer to a wire cake rack to cool completely. (The cookies can be stored in an airtight container at room temperature for up to 5 days.)