Preheat your oven to 325 degrees F.

Grease a 9x13 inch baking pan lightly and line it with parchment paper.

Cream together the butter, brown sugar, and vanilla until the mixture is light and fluffy.

Add the flour gradually, mixing until you form a soft dough.

Press this dough evenly into the prepared baking pan.

Bake for 30-35 minutes until the edges turn golden brown.

Remove from the oven and let it cool completely before proceeding with the next layer.

In a small saucepan, bring the water to a boil, then lower the heat to a gentle simmer.

Add the Jello powder, stirring constantly until fully dissolved, which will take about 4-5 minutes.

Mix in the sugar, continuing to stir over low heat until it fully dissolves without any grains left, taking another 4-5 minutes.

Take the pan off the heat and stir in the corn syrup.

Pour the mixture into a clean glass or metal bowl or the bowl of an electric mixer.

Refrigerate the mixture for about 30 minutes, stirring occasionally, until it is lukewarm.

Once it reaches lukewarm, beat the mixture at high speed with a whisk attachment for 10-12 minutes until it becomes very thick and fluffy.

Spread this marshmallow mixture over the cooled cookie layer and, if desired, sprinkle the top with dried coconut.

Refrigerate for 6-8 hours or overnight before slicing into bars.

Store the bars in airtight containers. They can be frozen for several weeks.