Line an 8x8 pan with parchment paper and set aside. Combine the cornstarch and powdered sugar, and cover the bottom and sides with half of this mixture.
Put gelatin and Bailey's into the mixing bowl of a stand mixer with the whisk attachment and set aside.
In a medium saucepan, combine sugar, corn syrup, salt, and water. Cover and heat over medium high heat for 4-5 minutes.
Uncover, and attach your candy thermometer to your pot, heating until the mixture reaches 240° F (about 5-10 more minutes). See the blog post above for tips on using a candy thermometer.
Remove from heat. Begin whisking the gelatin mixture in the stand mixer.
Very slowly pour in the corn syrup mixture while whisking. Continue whisking for about 12 minutes.
Spread the marshmallow mixture into the prepared pan.
Sprinkle remaining cornstarch mixture over top of the marshmallow mixture.
Let set for 4 hours.
Cut into cubes with a greased knife, or use a greased cookie cutter to cut into shapes.