Meringue 

1. Heat the oven to 225°F. Line a baking sheet with parchment.
2. If using granulated sugar, grind it in a blender until fine.
3. Beat the egg whites on low, increasing to medium, until they hold soft peaks, about 4 minutes. Add the cornstarch and increase to medium-high. Add the sugar a tablespoon at a time and beat until smooth and glossy, 4 to 6 minutes.
4. Fold in the vinegar and vanilla. Spoon the meringue into 6–8 mounds on the parchment, spacing them apart. Use the back of a spoon to make a small well in the center of each.
5. Bake for about 1 hour. Turn off the oven and leave the meringues inside to set and cool, about 1 hour. They should be crunchy on the outside and soft and marshmallow-y on the inside.

Poached Peaches

1. Combine the elderflower liqueur, water, sugar, lemon juice, and vanilla bean and seeds in a saucepan just large enough to hold the peaches. Heat slowly until the sugar dissolves.
2. Add the whole peaches. Cut a round of parchment to fit the pan, with a small hole in the center, and lay it over the fruit to keep them submerged. Cook at a gentle simmer until tender when pierced with the tip of a knife, about 15–20 minutes depending on ripeness.
3. Lift the peaches from the liquid and set aside to cool. Once cool enough to handle, slip off the skins.
4. Put the pan back over the heat and reduce the poaching liquid by about half, until lightly syrupy. Let cool.
5. Return the peaches to the syrup and chill for a few hours or overnight. To serve, lift them out, halve, and remove the stones. The poached peaches will keep in the fridge for 2–3 days.

To Serve

Place a meringue onto each plate with a dollop of crème fraîche. Place a poached peach half on top, then top with ice cream, more crème fraîche, and a spoonful of the reduced poaching syrup. Scatter with edible flowers.