Preheat the oven to 275 degrees F. Lightly butter a 9 1/2x14 1/2 jelly roll pan (slightly smaller pan works too).
Gently layer a piece of phyllo dough flat in the pan, allowing one side of the sheet to run up the sides of the pan. Brush with melted butter and then top with another sheet of phyllo dough, brush the top with butter. As you are working, overlap the sheets to create a border going up the sides of the pan. Repeat the layers until all the phyllo dough and around 4 tablespoons butter have been used.
Place in the oven and bake for 5 minutes. Remove from the oven. The dough will be puffy, but it will flatten as it cools. Increase the oven temp to 300 degrees F.
Add the peaches, nectarines and blackberries to a bowl. Add the remaining 4 tablespoons melted butter, honey, Kahlua (if using), vanilla and a pinch of salt. Toss well to combine. Arrange the fruit in an even layer on the phyllo dough, leaving the blackberries on top. Sprinkle the tart with brown sugar.
Bake for 20-25 minutes or until the blackberries have burst and the stone fruit is soft. Remove from the oven and drizzle with honey if desired.
To make the meringue, place the egg whites in the bowl of an electric mixer and whisk until stiff peaks form. Gradually add the sugar, whisking well, until the mixture is stiff and glossy. Now add the vinegar and vanilla bean, whisk until just combined.
Spoon the meringue into a piping bag or into a gallon size ziploc bag with the corner snipped off. Pipe the meringue onto the tart in cute little kiss dollops. Toast the meringue under the broiler or with a kitchen torch. If using the broiler, just be careful not to forget about the tart...it burns FAST. Do not leave it in there longer than a minute.
To serve, dust the tart with powdered sugar and garnish with cherries. Serve with ice cream if desired.
