Preheat the oven to 190°C/375F, or 170°C fans forced. Line two baking sheets with baking paper or silicon mats. If using chocolate bars, chop the chocolate using a chef's or santoku knife.
Partially cream the softened (but not melted) butter in a large mixing bowl using a spoon.
113 grams butter
Add in the sugar and cream by hand using a spoon or whisk for 2 to 3 minutes.
125 grams white sugar
Add in the egg and vanilla. Beat together with a spoon or whisk until well combined, this will take about 2 to 3 minutes.
1 teaspoon vanilla, 1 egg
Add in the flour, baking soda and salt. Mix through until most of the flour has been mixed into the wet ingredients.
½ teaspoons baking soda, ¼ teaspoon salt, 160 grams flour
Toss in the chocolate and mix through. Then knead the biscuit dough by hand a few times to make sure all the ingredients are well combined.
150 grams chocolate
Using a cookie or ice cream scoop, scoop out portions of cookies and place them on the baking sheet about 3 inches or 7cm apart. Alternatively, roll out balls of dough about 3cm or just over an inch in diameter. Bake for 10-12 minutes. Allow the cookies to cool on the baking sheet before lifting them onto a cooling rack to cool completely.