Ingredients:

For the cookie base
1 cup butter room temperature
1/2 cup brown sugar
1 tsp vanilla extract
2 cups flour
For the marshmallow top layer
1 cup water
2 pkg cherry Jello powder (4 oz/ 85 g each)
1 1/2 cups sugar
1/4 cup corn syrup preferably light
1/2 cup dried unsweetened or sweetened coconut to garnish top; optional
3/4 cup chopped maraschino cherries

Instructions:

For the cookie base.
Preheat oven to 325 degrees F.Lightly grease a 9×13 inch baking pan and line it with parchment paper.
Cream the butter, brown sugar and vanilla well until light coloured and fluffy.
Fold in the flour to form a soft dough.
Press the dough evenly into the prepared pan.
Bake for 30-35 minutes until golden brown around the edges.
Remove from oven and cool completely before adding the top layer.
To prepare the marshmallow layer.

NOTE: You are going to want to keep the temperature on low throughout this stage. You don’t want the mixture to boil; just keep the heat steady to allow you to fully dissolve the jelly powder and sugar.
In a small saucepan bring the water to a boil and reduce the burner setting to low.
Add the 2 pkg of Jello powder and stir continuously until it is completely dissolved. This can take 4-5 minutes.
Add the sugar and again, continue to stir over low heat until the sugar is fully dissolved with no sugar grains left at the bottom of the pan. This may take 4-5 more minutes or so.
Remove from heat and stir in the corn syrup.
Transfer the mixture to a very clean glass or metal bowl or the bowl of your electric mixer.
Chill in the fridge for about a half hour, stirring occasionally until the mixture is just lukewarm. It should not be hotter than lukewarm, nor should it me too cold.
When the jello mixture reaches the lukewarm point, begin beating it at high speed with the whisk attachment on your electric mixer. Beat for 10-12 minutes or until very thick and fluffy.
Fold in the chopped cherries
Spread the marshmallow layer over the cooled cookie layer and sprinkle with coconut if you like.
Refrigerate for 6-8 hours or overnight before cutting into cookie bars.
Store in airtight containers. These freeze particularly well for several weeks.

From: https://www.rockrecipes.com/cherry-marshmallow-cookie-bars/