1. Heat your oven to 250°F. Add egg whites to the bowl of a stand mix and whip on medium-low speed with the whisk attachment until foamy, 3-5 minutes.
2. Increase the speed to medium-high and add granulated sugar one tablespoon at a time at 15-second intervals until all the sugar has been added and the mixture has soft peaks. Add lemon juice and cornstarch and continue running the mixer until you’ve achieved stiff peaks.
3. Prepare your Holy Sheet by dotting a small amount of the pavlova meringue in each corner to hold down the parchment paper when you’re spreading the meringue mixture.
4. Using an offset spatula, spread your pavlova mixture across your baking sheet into an oval or rectangular shape, keeping it around ¾-in. height.
5. Bake for 2 hours, and then, without opening the oven, turn the oven off and let the pavlova rest for 3 hours before taking out and decorating.
6. Make the whipped cream. Dissolve gelatin by adding the cold water to a bowl and sprinkling the gelatin on top; let that sit for 5 minutes. Microwave the gelatin for 30 seconds or until fully dissolved and liquid-y. Optional if not using gelatin.
7. Add the heavy whipping cream, powdered sugar, vanilla paste, and salt to the bowl of a stand mixer fitted with the whisk attachment and beat on medium speed until soft peaks form.
8. Pour the liquid gelatin mixture into the whipped cream and continue whisking until you achieve stiff peaks. Optional if not using gelatin.
9. Before serving, spread the whipped cream over the pavlova meringue and decorate with fruit, jam, lemon curd, etc. as desired. Leave the pavlova on the sheet pan for an easy and beautiful presentation.