Grease an 8x11 pan.
Melt butter in a large heavy bottomed pot.
Add the Bailey's and stir it into the melted butter.
Add the marshmallows. Stir to coat them in the melted butter/Irish Cream mixture. Stir over medium-low heat until the marshmallows are melted and smooth. Remove the pot from the heat.
Add in the Lucky Charms and reserved marshmallows. Stir quickly to combine. Immediately press into greased 8x11 pan. Press down on the top with a greased spatula to flatten and smooth out.
Allow to cool, then cut and serve!