Line a large, rimmed baking sheet with parchment paper or a Silpat® mat. Set aside.
In a large mixing bowl, whisk together the butter, light brown sugar, and white sugar until smooth and fluffy, about 2-3 minutes.
Add the egg and vanilla; continue whisking until smooth.
Gently fold in the flour, baking soda, and baking powder until the mixture is combined. Then gently fold in the diced strawberries.
Divide the mixture into 12 cookies and shape them into balls. Place on the prepared baking sheet, pressing an indent in the centre of each cookie.
Chill the cookies in the refrigerator for 30 minutes.
Preheat the oven to 350°F (175°C).