Pre-heat oven to 375 degrees and line two cookie sheets with parchment paper or Silpats.
In the bowl of a stand mixer (or a large bowl with a hand mixer), cream together the butter and sugars until light and fluffy, 2-3 minutes.
Add eggs and vanilla and beat until smooth.
In a separate medium bowl, whisk together flour, cinnamon, baking soda, and salt.
With mixer on low, gradually mix in the dry ingredients until just combined, taking care not to over-mix.
Gently fold in chopped dark chocolate and mini marshmallows.
Drop about 1 ½ Tbsps of cookie dough onto prepared baking sheets (I like to use a cookie scoop), placing dough about 2 inches apart.
Bake cookies for 8-11 minutes, until cookies are just turning golden. Let cool on the pan for a couple minutes before moving to wire racks to cool completely.