Vanilla cake, filled with grape jam, with Balsamic Caramel Swiss Meringue Buttercream.
Bring it to a boil, then reduce the heat to medium low, and cook for about 10 minutes, stirring constantly.
Mix cornstarch and water, add it to the jam mixture. Let it come back to a boil and keep stirring and cooking for a few more minutes until it thickens. Don't stop stirring at this point, or the cornstarch will clump up.
Whisk whites and sugar until they temp 140F. Basically you are looking to melt the sugar granules, and also make it so the egg white is in a safe temperature to be consumed.
Whip with the whisk attachment for about 2 minutes at medium speed, until the mixture looks white, and thicker. At this point, raise speed to high and continue to whip until fluffy and doubled in size. Meringue should have stiff peaks. It can take anywhere from 5-10 minutes to obtain stiff peaks.
You probably won't have leftover buttercream, but if you do, you can simply store them in the fridge for up to 4 days, or in the freezer, for up to 2 months. Remember to package it really well in sealed air tight containers, or zip loc bags, before freezing.
*You can make this jam without the cornstarch, but it might be slightly thinner. I like the jam to be really thick for cake filling. If you don't want to use cornstarch, simply cook the jam for about 30 minutes with just the grapes, sweetener, and lemon juice, until thick, and until a thermometer registers 220 F.
**This recipe will make more caramel than what you need for the Swiss Meringue Buttercream. You can store any leftovers for up to 1 month in the fridge, and up to 3 months in the freezer. Or use it to decorate the top of the cake like I did!