In another bowl, combine the melted butter and sugar. Whisk vigorously until the sugar is mostly dissolved. Set aside for 5 minutes to cool.
225 grams butter, 220 grams light brown sugar, 100 grams white granulated sugar
Add in the vanilla and eggs. Whisk vigorously to combine fully.
1 tablespoon vanilla extract, 2 eggs
Pour the wet ingredients into the dry ingredients. Using a wooden spoon or rubber spatula, mix the cookie dough until all the flour is incorporated and a soft cookie dough forms.
Line a baking tray or plate with baking paper or parchment paper. Portion the cookie dough out into 2 tablespoon-sized balls. Roll the cookie dough balls until round. Cover with cling-film or plastic wrap and pop into the fridge. Alternatively, you can line an airtight container with baking paper, and place the cookie dough balls into the container.
Let the cookie dough balls rest in the fridge for at least 20 minutes to 24 hours.
Preheat the oven to 180°/350°F (160°C fan) - this will take about 20 minutes. Line a baking tray or two with baking paper or parchment paper.
Place the chilled cookie dough balls on the baking tray about 2 to 3 inches apart. Bake for 15 to 20 minutes. My cookies were done at the 17-minute mark.
Allow the cookies to cool on the baking tray for 5 minutes before lifting them gently onto a wired cooling rack to cool completely.
All temperatures stated are for conventional ovens. Decrease the temperature by 20°C/25°F or gas mark 1 for "fan" or air-fryers.
Notes
225 grams of butter is equal to two stick of butter and is 25 grams less than a metric cup of butter.
The cookie dough may initially look a bit too soft, but as the dough stands the butter will become more solid, and the oats and flour will absorb the moisture in the cookie dough.
The cookie dough must rest for at least 20 minutes in the fridge, but the flavor is really great after a 24-hour chill in the fridge.
For picture-perfect round cookies, use a large cookie cutter or bowl and scoot around the edges of the cookies into a perfect circle while they are still hot.
You can dip the rolled cookies into additional chocolate chops or chunks before baking for that goey chocolate on top of the cookies look.
Reduced Sugar Variation (for a full batch)
25% reduction - 165 grams (¾ cup) of brown sugar, and 75 grams (⅓ cup)of white sugar.
50% reduction- 110 grams of brown sugar (½), and 50 grams (¼) of white sugar.
Because of the sugar reduction, the cookies won't spread as much during baking. If you want a flatter cookie, then press down the cookie balls to about 1cm tall before chilling.
Storage and Freezing
Store the baked cookies, once completely cooled, in an airtight container for up to a week.Baked, cooled cookies can be frozen in an airtight container for up to 3 months.Portioned cookie dough balls can be stored in an airtight container for up to 3 months. To bake, preheat the oven and bake from frozen. You may need to add 2 to 3 minutes to the baking timing.