Prepping for Christmas before Halloween

I am on the hunt for a giftable jar cookie recipe. For our girls club Christmas party I like to have stations so the girls can cycle through, make an ornament or two, make a treat, play a game, do a service project, etc. It splits them up and makes the night more fun. As of this writing it's October and yes I'm planning for December - that's how I roll, always. I tried this recipe out to see if it was a winner. It absolutely was, but it didn't fit in my container... so well working on that part. I love that all you make the dry mix, send it home, and the girls can make cookies with their family for Christmas. This recipe was an absolute hit with my family, it was easy and not many things needed to be added, just melted butter, vanilla, and an egg. This isn't my only test, I have another on the horizon - we'll see if that fits the bill or not.

Cookie Mix in a Jar (giftable)
Ingredients
2 cups + 2 Tablespoons all-purpose flour (265g)
1 Tablespoon cornstarch
½ teaspoon baking powder
½ teaspoon baking soda
½ teaspoon salt
½ cup dark brown sugar¹ firmly packed (100g)
½ cup light brown sugar¹ firmly packed (100g)
¼ cup granulated sugar (50g)
1-1 ½ cups mix-ins I used a blend of Christmas-colored M&Ms, semisweet chocolate chips, and white chocolate chips.

To be added by gift recipient:
12 Tablespoons unsalted butter melted
1 large egg
1 teaspoon vanilla extract

Instructions
In a large bowl, combine flour, cornstarch, baking powder, baking soda, and salt, and whisk until well-combined.
Use a large spoon to spoon the flour-mixture into the bottom of your mason jar. Tamp down to pack down the flour as much as possible. Use your spoon to create a straight line of flour directly against the glass (so you have nice, even layers) but don’t worry if some of the flour in the middle is uneven or mounded. If you happened to get a lot of flour on the sides of the jar, you can use a paper towel or pastry brush to wipe down the excess flour.
Add dark brown sugar to the jar and use your spoon to firmly pack over the flour. Again, aim for clean straight edges against the glass.
Top with light brown sugar and firmly pack over the dark brown
Top with granulated sugar.
Top sugar with add-ins, filling to the very top/brim of the mason jar. You want all ingredients to be tightly packed in so they don’t shift during any transportation.
Top with mason jar lid and seal tightly. Print off printable instruction tag (find link to printable in the "equipment" section at the top of the recipe) and attach to jar with baker’s twine or ribbon.

Instructions for Gift Recipient:
Preheat oven to 350F. Let butter cool until no longer warm to the touch. Stir together cooled butter, large egg, and vanilla extract. Add all ingredients from jar and stir well until completely combined (make sure to break up any clumps).
Drop by rounded 1 ½ Tbsp-sized scoops onto ungreased cookie sheet and bake for 9-11 minutes. Cool on baking sheet and enjoy!