Prepare a 9 x 13-inch baking pan by spraying liberally with cooking spray. In a small bowl, whisk together 1/4 cup cornstarch and 1/4 cup powdered sugar. Sift a small amount evenly across the baking pan, and set aside the rest.
Combine 1.5 ounces freeze dried strawberries and 1 tablespoon loose Earl Grey tea leaves in a food processor. Pulse repeatedly until all the strawberries and tea leaves have crushed into a fine powder. Set aside. Pour 1/2 cup cold water into the bowl of a freestanding electric mixer fitted with a whisk attachment. Sprinkle 3 envelopes powdered gelatin over the water, and give the mixture a quick whisk to make sure all the gelatin granules are wet. Let stand until the gelatin softens and absorbs water, at least 15 minutes. While the gelatin is blooming, combine 2 cups granulated sugar, 2/3 cup light corn syrup, 1/4 teaspoon kosher salt, and the remaining 1/2 cup water in a medium, heavy-bottomed sauce pot. Use a heatproof rubber spatula to stir over medium-low heat until the sugar dissolves, scraping down the sides of the pan. Attach a candy thermometer to the side of the pan, increase the heat to medium-high, and bring the syrup to a boil. Boil without stirring until the syrup reaches 240 (F). When the syrup reaches 240 (F), immediately pour the syrup into a liquid measuring cup.
Turn on the mixer to its lowest speed and slowly pour the hot syrup into the mixer bowl with the gelatin mixture in a thin stream down the side of the bowl — avoid pouring the syrup onto the whisk, as it may splash and send boiling syrup everywhere! Once the syrup is completely added, gradually increase the mixer speed to its highest setting and beat until the mixture is very thick and stiff, about 15 minutes. In the last minute, add the strawberry and Earl Grey powder (from the 2nd step) and continue whisking for another minute, until the mixture is a pale pink color.
Scrape the marshmallow mixture into the prepared pan, using a wet offset spatula to smooth the top — this is probably the most difficult part of the recipe as the marshmallow mixture is going to be incredibly sticky. It really helps if your spatula is wet! It's also not the world's biggest deal if the mixture isn't perfectly smooth — you're going to end up inverting the marshmallow block.
Sift a generous dusting of the cornstarch and powdered sugar mixture (from the 1st step) over the marshmallow mixture and let stand uncovered at room temperature until firm, about 4 hours, but preferably overnight.