Place the cherries, sugar, and balsamic into a small saucepot or saucier. Bring the ingredients to a boil over medium-high heat. Lower the heat to medium and gently boil for 15 to 20 minutes, or until the liquid is slightly thickened and syrupy, leaving about ½ cup of liquid in the pan.
Strain the cherries through a sieve over a bowl, reserving all the liquid/syrup. Resist the temptation to press more liquid out of the cherries; leave them “plump” for a burst of flavor with each bite.
Set the cherries and their syrup in the refrigerator until ready to use.
Preheat the oven to 325 degrees F. Grease and line 2 8” round cake pans with cake release/spray/”cake goop” and line with parchment paper. Grease the parchment. Set the pans aside.
In a stand mixer bowl fitted with the paddle attachment, add the eggs, milk, oil, and extracts. Turn the mixer to low and combine well. (Alternatively you can do this with a hand-held mixer.)
Add the cake mix and espresso powder if using. Combine on low just until all the ingredients are well combined, scraping the bowl and paddle as needed.
Divide the batter evenly into the greased pan. (I use a kitchen scale to measure each pan so that they are equally filled with the batter.)
Bake in the oven for 22 to 25 minutes, or until the cakes are done. Check by inserting a toothpick into the center of the cakes; it should come out clean.
Remove the cakes to cool at room temperature for 20 minutes. Invert the cakes onto a cooling rack and cool to room temperature. (At this point, you can wrap them in plastic wrap and freeze for up to a month. You may also freeze the cakes for a few hours until ready to use. That little bit of time will help keep the cakes moist. This step is optional.)
Before assembling, whip the heavy cream, sugar, and vanilla on medium speed until beginning to thicken. Turn the speed to high and whip until stiff peaks.
To assemble, place one cake layer on a cake stand. Brush the layer with some of the strained cherry-balsamic syrup. Pipe or spread half of the whipped cream on top of the cake. Scatter half of the cherries gently over the whipped cream. (I find this is easier to do by hand instead of them dropping by clumps into the whipped cream.)
Lay the second cake gently on top of the cherries. Brush the top layer with some of the syrup. Pipe the remaining whipped cream on top. Scatter the remaining cherries over the top of the whipped cream. Optional, you can drizzle leftover syrup from the cherries onto the top of the cake and/or each serving.
Cut and serve.