- Add the butter to a saucepan and melt over low to medium heat, stirring consistently. The butter will start to foam; continue stirring until it turns a golden brown/amber color.

- Carefully transfer the browned butter into a heat-safe dish and let it cool for 10-15 minutes.

- In a bowl, whisk together the cooled brown butter, caster sugar, and light brown sugar until well combined.

- Add the egg and vanilla extract, whisking until the mixture is smooth and fully integrated.

- Fold in the plain flour and baking soda until just combined.

- Gently fold in the chocolate chips and crushed digestive biscuits or graham crackers.

- Take 1-2 heaped tablespoons of cookie dough (approx. 50g-60g) and flatten it in your hand.

- Place a marshmallow in the center of the dough and wrap the dough around it, ensuring the marshmallow is completely covered.

- Top the dough balls with additional chocolate chips and crushed biscuits if desired.

- Chill the cookie dough balls in the refrigerator for 1-2 hours.

- Preheat your oven to 160°C (320°F).

- Arrange the chilled dough balls on a baking sheet, ensuring there is enough space between each cookie.

- Bake for 14-17 minutes, adjusting the time based on your preferred level of gooeyness.

- Allow the cookies to cool slightly on the baking sheet before transferring them to a wire rack to cool completely.

- Enjoy your delicious s’mores cookies!