Preheat the oven to 350°Fahrenheit/175°Celsius. Line 2 baking sheets with parchment paper
In a large bowl, whisk the cooled melted butter with the two sugars until smooth.
1 ½ sticks unsalted butter, ½ cup white sugar, 1 cup light brown sugar
Add the egg, egg yolk, and vanilla bean paste and whisk again until well combined.
1 large egg, 1 large egg yolk, 2 teaspoons vanilla bean paste
Add the flour, baking soda, baking powder, cornstarch, and salt. Use a wooden spoon or rubber spatula to fold everything together. It takes some time to get everything smooth. Don't overmix!
Use a 1 ½ tablespoon cookie scoop to scoop out the cookie dough. Place on the lined baking sheet about 3 inches apart. Bake for 9-12 minutes. Any cookies that aren't being baked right away should be placed in the fridge.
To make these cookies bakery worthy, take a small handful of extra mini m&ms and carefully press those on the cookies when they come out of the oven. Use a biscuit cutter to scoot the cookie if it isn't perfectly round and sprinkle over some flaky sea salt.
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. .Butter: I use European style butter, like Kerry Gold, in my recipes. This will make your finished bake much creamier and richer.Salt: If you don’t have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt.M&Ms: you can use regular m&ms though if you find they're too big I recommend chopping them up.Chocolate Chips: want more of a chocolate kick? Use half the amount of mini m&ms and add an equal amount of mini chocolate chips. Storage: keep the baked cookies in a tupperware for up to 1 week at room temperature. Freeze unbaked cookie dough balls for up to 2 months. When ready to bake, take them out of the freezer and bake at the same temperature as above but for an extra minute or two.