Line a 13″x9″ baking pan with saran wrap. Sprinkle liberally with powdered sugar. Set aside.
In a standing mixer with a whisk attachment, pour ½ cup water and gelatin into bowl. Mix and allow for gelatin to “bloom” for at least 5 minutes.
Combine sugar, corn syrup, salt, and remaining ½ cup water in a medium saucepan. Attach a candy thermometer to the side of the bowl. Heat over medium heat, stirring with a heat-safe spatula. Once the sugar is dissolved, increase the heat and boil without stirring until the mixture reaches 240°F, about 8 minutes. If you don’t have a candy thermometer, just allow the mixture to boil for 8 minutes. Immediately remove from heat.
Turn the standing mixer to low speed and slowly pour the sugar mixture into the bowl with the gelatin mixture. Once added, increase speed to high and whip for approximately 15 minutes, until the mixture becomes very thick and stiff. Add the vanilla extract in the last minute of whipping.
Pour mixture into prepared baking pan, smoothing the top with a spatula. Knock the pan on a counter to release any air bubbles from within the mixture. Sprinkle top with powdered sugar and allow to cool for at least 4 hours.
Make the homemade salted caramel
In a medium saucepan, heat the sugar on medium heat for about 5 minutes. Use a spatula to occasionally stir the sugar, getting to the bottom of the pan. At first the sugar will be lumpy, but will soon melt and start turning a brownish color. Don’t stir too often, just enough to keep everything evenly cooking.
After 5 minutes, the sugar should become fully melted. Once it becomes an amber hue, remove from heat immediately and stir in butter. The mixture will violently bubble. You’re doing it right.
Use your spatula to stir the butter and sugar until they melt together completely. This can take 1-2 minutes.
Next, pour in the heavy cream and sea salt. Use your spatula to stir until everything is combined. Place back on the stove for about 30 seconds, stirring the whole time. Remove from heat and refrigerate until cool.
Assemble the mallows
Once everything is cooled and ready, liberally coat a work surface with powdered sugar and place the marshmallow on top. Rub the powdered sugar all over the marshmallow. Cut the block into 3″x3″ squares (you will have a 1 inch strip left to munch on!). Rub each square into the powdered sugar to coat. Place marshmallows on a parchment paper-lined cookie rack.
Dollop a liberal tablespoon of salted caramel onto the top of each marshmallow, leaving a small border around the edges.
Melt the chocolate and oil in a shallow microwave-safe bowl in 20-30 second increments, stirring in between each time. Dip each marshmallow into the melted chocolate, salted caramel side first (trust me!) before dipping the other sides. Shake to remove excess chocolate, and set back on the cookie rack. Allow to cool for ~3 minutes before sprinkling with graham cracker pieces. Allow for chocolate to harden completely before serving.