Preheat your oven to 200F. Line two baking sheets with parchment paper & set aside.
In large mixing bowl (or bowl of your stand mixer) whisk together the egg whites, salt & corn starch. When the egg whites become foamy, with the mixer still running, pour in the sugar. Beat an additional 2-3 minutes on high, until very stiff peaks form. Pour in the vinegar & vanilla extract. Beat one last time until combined.
Spoon out big dollops of meringue onto your baking sheet & using the back of a spoon, create little cavities in the center.
Bake for 2 hours, or until they are dry & crisp. Turn off the heat & allow the meringues to come to room temperature.
While they are cooling, in a small saucepan over medium heat, simmer the citrus juice until it reduces by half, about 3-5 minutes. Set aside to cool slightly.
In large mixing bowl, add the softened butter & sugar. Beat until light & fluffy, about 2 minutes. Add the egg yolks & beat the mixture together. Add the eggs & beat again until all is incorporated. Stir in the salt & then in a few batches, add the citrus juice & ginger (the mixture will look curdled).
Rinse out the small saucepan you used earlier & fill it with a few inches of water. Bring the water to a simmer & place a stainless steel bowl on top of it with the curd mixture inside. Stir constantly & heat the curd slowly enough that the sugar has time to dissolve & the mixture becomes cohesive (about 10 minutes). Pull the curd from the heat when it's thick enough to coat your spoon (if using a thermometer it will read 165F). The curd will thicken as it cools.
Run curd through a sieve into a chilled bowl 3x.
Place the curd inside the cavities of your meringues, top with fresh fruit & powdered sugar. Serve & enjoy!