Preheat the oven to 350 degrees F. Place an oven rack in the middle position. Lightly spray a cupcake pan with cooking spray or fill it with cupcake liners first and then lightly spray them with cooking spray.
In a medium bowl, whisk together the flour, cinnamon, baking powder, salt and cornstarch. In a separate bowl, whisk together the heavy cream and bourbon.
In a stand mixer with the paddle attachment, cream the butter and sugars together on low speed for 5 minutes. Add the eggs, one at a time, allowing each egg to incorporate before adding the next one. Use a spatula to scrape down the side of the bowl. With the mixer still on low, quickly alternate between adding the flour mixture and liquid ingredients over approximately 30-60 seconds. Scrape down the sides of the bowl all the way to the bottom and then turn the mixer on medium speed for 30 seconds. Stir in the chopped peaches by hand.
Evenly distribute the batter between the 12 cupcake tins. Bake for approximately 22 minutes, or until a toothpick comes out clean. Allow the cupcakes to cool for 5-10 minutes, then carefully remove them from the pan to a cooling rack. The cupcakes can stay in the refrigerator for up to 48 hours before frosting, if desired.
Prepare the buttercream:
Place the pitted peach in a sturdy blender and puree until smooth. Peeling it first is optional but recommended if using an older blender.
Add sugar and water to a medium sized sauce pot. Cover and turn the heat to high. Once the liquid begins to simmer and steam has developed, remove the cover (this helps prevent crystallization). Using a candy thermometer, cook the sugar to the soft boil stage, 235-240 degrees F.
While the sugar is simmering, whisk the eggs on high speed in a stand mixer with the whisk attachment until they reach a soft peak.
Turn the mixer speed down to medium low and very slowly pour the syrup down the side of the bowl into the egg whites. Don’t pour the hot syrup directly into the meringue or the eggs might scramble.
Once the syrup is incorporated, turn the mixer to high speed and allow the mixture to continue forming a stiff peak while cooling down. Mix on high until the meringue has reached room temperature. Optionally, ice packs can be placed around the bowl to speed up this 15-20 minute process.
Once the meringue is room temperature, very slowly begin incorporating the soft butter on medium speed. Once all of the butter has been incorporated, turn the mixer up to high high and very slowly add 1/4 cup of the peach puree, bourbon and food coloring, if using. If the mixture starts to curdle at any point, microwave 2 tablespoons of it for 5-7 seconds and then incorporate it back into the buttercream on high speed. That should bring it back together.
Pipe the buttercream frosting onto the cupcakes and serve.
Additional chopped peaches (up to 1 cup) may be added to the cupcake batter. Just note that this will likely create leftover batter.All granulated sugar may be used in the cupcakes as opposed to 50% granulated sugar and 50% brown sugar. The cupcakes will be slightly paler in appearance but will still taste excellent.