Line a baking sheet with a piece of parchment paper (important). Draw a 7-inch circle. Preheat oven to 225 degrees F.
In a stand mixer, on medium speed, beat the egg whites with the whip attachment until foamy. Add the cream of tartar and beat until the whites are at soft peak. Slowly add 1/2 cup sugar in a constant stream as the eggs are whipping. Add the cornstarch, salt, vanilla bean seeds, and lemon juice. Beat on medium-high until egg whites are glossy and hold a stiff peak when lifted out of the bowl.
Spoon meringue onto your circle, and spread to the eggs of the circle, gently. Bake for 1 hour and 15 minutes. Then turn the oven off, open the oven door slightly ajar, and allow meringue to stay in the cooling oven for another hour. This will further dry the meringue and prevent it from collapsing. (The outside of the meringue will feel firm to the touch, if gently pressed, but as it cools you may get a little cracking and you will see that the inside is soft and marshmallowy.)
When ready to serve, pour the cream into a large bowl and add the remaining two teaspoons sugar. Whip until it forms soft peaks. Spread it on top of the cooled and set meringue, then top with blackberries, lemon zest and honey.