Preheat the oven to 200°F. Line an 11 x 17-inch baking sheet with parchment paper.

Pour the egg whites into the clean bowl of an electric mixer with the whisk attachment. Mix on low speed for 10 to 15 seconds to loosen up the egg whites. Gradually increase the speed until light and foamy.

Slowly add the sugar, 1 tablespoon at a time, and continue mixing on high speed until the meringue is glossy and stiff peaks form, 4 to 5 minutes.

Add the vanilla, cornstarch, and vinegar and mix a few more times to incorporate.

Using a rubber spatula, gently transfer the meringue onto the prepared baking sheet and spread to form a rectangle.

Transfer to the oven and bake until slightly golden and set, 55 to 60 minutes. Remove from the oven and cool.

In the meantime, prepare the cream: Place the metal bowl of a stand mixer and whisk attachment in the freezer for at least 10 minutes.

Remove the chilled bowl and whisk from the freezer, pour in the cream and bitters, and whisk on medium speed to form soft peaks, about 2 minutes.

Transfer the whipped cream to a separate bowl and refrigerate until ready to assemble.

Place the strawberries, lemon juice, and sugar into a medium bowl and stir to combine. Allow the berries to marinate for at least 15 minutes.

Assemble the merengón: Transfer the baked meringue onto a large platter. Spread the cream all over the surface, leaving about a ½-inch border, pizza style.

Scatter the strawberries and drizzle their juices over the cream and garnish with the dandelion petals, if using. Cut into messy squares and serve.