Method

• 1.
  Preheat oven to 200°C/180°C fan-forced. Grease a large baking tray and line with baking paper. Place sweet potato on tray, drizzle with oil and toss to combine. Bake for 20-25 minutes, until lightly caramelised and cooked. Cool completely on tray.
• 2.
  Meanwhile, place butter in a small saucepan over medium-high heat and cook, swirling pan, for 2-3 minutes, until butter begins to foam and brown. Cool in pan to room temperature.
• 3.
  Place sugars and cooled butter in a stand mixer fitted with the paddle attachment and beat on low speed until combined. Add egg, egg yolk and vanilla and beat until combined and smooth. Add flour and bicarb and beat until combined. Add chocolate and three-quarters of the sweet potato and beat until combined.
• 4.
  Reduce oven temperature to 180°C/160°C fan-forced. Grease 3 large baking trays and line with baking paper. Divide mixture into 14 portions (about 70g each) and roll each portion into a ball. Place balls on prepared trays, leaving 3cm between each (cookies will spread), and press to slightly flatten.
• 5.
  Scatter with extra choc chips and remaining sweet potato and gently press to adhere to tops of each cookie. Chill for 15-18 minutes to firm up slightly.
• 6.
  Bake for 12-15 minutes, until starting to turn golden on the edges. Remove from oven and allow to rest on tray for about 10-15 minutes before serving. Cookies will crisp up but still have a chewy and caramelised texture.