For the cookies: Whisk together 5 cups flour, baking soda, and baking powder in a bowl.
In a stand mixer, cream butter and sugar until light and fluffy, around 3 minutes.
Add eggs, one at a time, beating well to incorporate.
On low speed, beat in vanilla and sour cream.
Add flour mixture and beat on low until combined.
Then you will want to add up to 1 more cup of flour, 1/4 cup at a time, until a good rolling consistency is met. It will be a sticky, soft dough.
Divide dough into two equal parts. Flatten into 1 1/2-inch thick rectangles and wrap with plastic wrap. Chill overnight.
On a generously floured surface, roll dough out to 1/4-inch thickness. Cut with cookie cutter and transfer to a parchment paper-lined baking sheet. Repeat until all dough is gone.
Bake in a preheated 425* oven for 7 to 8 minutes until just slightly golden. Transfer to a wire rack to cool.
For the frosting: cream butter and vanilla together.
Slowly add powdered sugar and meringue powder.
Add heavy cream a tablespoon at a time until desired consistency is met. Add food coloring, if you want.
Frost completely cooled cookies and add sprinkles. Store in airtight container.