Preheat the oven to 425 F (218 C). Line a baking sheet with parchment paper. Clean and dry 3 medium sweet potatoes. Pierce the sweet potatoes 5 - 6 times all around the potato. Roast for 40 - 45 minutes or until fork tender. Cool to room temperature, scoop out the sweet potato flesh into a food processor. Blend until smooth. Measure out 2 cups of pureed sweet potato. Alternatively, use canned sweet potato. 3 medium sweet potatoes
In a mixing bowl whisk together the flour, oats, baking soda, cinnamon, pumpkin pie spice and salt until well combined.
2 cups (240 g) all purpose flour, 1½ cups (120 g) quick cooking, old fashioned or rolled oats, 2 teaspoons ground cinnamon , 2 teaspoons pumpkin spice, 1 teaspoon baking soda, ½ teaspoon salt
In a microwave safe bowl heat slices of cold from the fridge butter for 30 seconds. The butter should be mostly solid with softened edges. Transfer the softened butter into a large mixing bowl fitted with a paddle attachment. Add the light brown sugar and granulated sugar. Mix the butter and sugars on medium speed for 2 - 3 minutes or until the butter and sugars are well combined. 10 tablespoons (141 g) cold unsalted butter, sliced, ¾ cup (150 g) light brown sugar, ½ cup (100 g) granulated sugar
On low, cream in the sweet potato puree, egg yolk and vanilla extract until smooth and well combined. With the mixer on low, add the dry ingredients and chocolate chips into the wet a little at a time. Mix until just combined.
1 large egg yolk, 2 teaspoons (10 ml) vanilla extract , 1½ - 2 cups chocolate chips, optional
Cover the cookie dough and transfer to the fridge to chill for 30 minutes - 2 hours. The longer the chill, the chewier and softer the cookie.
Preheat the oven to 350 F (177 C) for about 30 minutes before baking the cookies. Line a large baking sheet with parchment paper. Using a medium cookie scoop (2 tablespoons, 30 ml), scoop the oatmeal sweet potato cookie dough into balls and place them onto the lined baking sheet about 3 inches (8 cm) apart. Top with more chocolate chips if you like.
Bake the sweet potato cookies at 350 F (177 C) for 10 - 12 minutes or until the edges of the cookies are set. The center of the cookies will be slightly puffed up.
Remove the cookies from the oven. Reshape any cookies using a biscuit or cookie cutter slightly wider than the cookie. Place the cutter over the cookies so the edges of the cookie are inside the cookie/ biscuit cutter. In a circular motion, gently nudge the edges back into a round shape. Cool the chewy oatmeal and sweet potato cookies on the baking sheet for 10 minutes. Then transfer to a cooling rack to cool completely to room temperature and enjoy.