Preheat oven to 180c or 350F
Melt the butter in the microwave for 30 seconds, then let it cool
Add the sugar, vanilla extract, yogurt and cooled melted butter into a bowl and whisk well
Add the dry ingredients (minus the marshmallows) and using a spatula, mix until a cookie dough forms
Scoop out 9 cookies- flatten each cookie dough scoop and add 3 mini marshmallows in the middle. Form a ball with the cookie dough with the marshmallows inside and slightly flatten on the baking sheet. Top with extra milk chocolate.
Bake for 8-10 minutes (I usually take them out on the 9 minute mark)
Let it cool in the pan for 10-15 minutes
Optional: Top with some flaky sea salt