Warm the heavy whipping cream in a medium sauce pan over medium-high heat, add in the cinnamon and vanilla extract. Whisk to combine.*
Add the chopped white chocolate into a large mixing bowl or into the bowl of a stand mixer. Pour the warm cream mixture over the white chocolate and stir gently until all chocolate is melted. Cover and chill for at least 4 hours (prepare cookies while ganache chills).
After chilling, use a stand or hand mixer fitted with a whisk attachment and whip for 4-6 minutes until stiff. After a few minutes of whipping check the consistency of the ganache, you want a stiff frosting that will hold its shape.* If desired transfer to a piping bag. Keep chilled until ready to use.
For the Snickerdoodle Cookies:
In the bowl of a stand mixer fitted with the paddle attachment, cream butter and sugar for 4-5 minutes until light and fluffy. Add in the eggs and vanilla. Cream for 1-2 minutes longer.
In a small mixing bowl combine the flour, cream of tartar, baking soda, and salt. With the mixer on low slowly add in the dry ingredients into the wet ingredients and mix until evenly incorporated.
Using a portion scoop or measuring spoon, scoop 1 oz. scoops of dough. Transfer to a sheet pan. Chill for 30 minutes, or overnight if needed. Preheat oven to 350 degrees F.
In a small mixing bowl combine the sugar and cinnamon. Roll each chilled cookie into the sugar mixture. Arrange 2 inches apart on a lined sheet pan. Bake at 350 for 9-11 minutes until slightly golden brown. Allow to cool on the cookie sheet for a few minutes before transferring to a wire rack. Allow cookies to cool completely before adding ganache.
Pipe or spread the whipped ganache between two snickerdoodles. These are best enjoy the same day, but will keep for 2-3 days in the fridge if stored in an airtight container.
Notes
*Since we are whipping this ganache heavy whipping cream must be used, do not substitute half and half.*You just need to warm the cream enough to melt the chocolate, watch carefully so mixture doesn't scold. *Careful not to over whip the ganache, the cream will break if overwhipped creating a grainy texture. *Unused ganache will keep in an airtight container in the fridge for up to a month.