For the cake:
Preheat oven to 350F. Grease an 8-inch round cake pan and line the bottom with baking paper.
In a medium bowl, whisk together flour, sugar, salt, baking soda and cocoa powder.
Using a spoon, make 3 wells in the dry ingredients, one large well and two smaller wells. Pour the grapeseed oil into the largest well, the vinegar into one of the smaller wells, and the vanilla extract into the last well. Pour the cold water over everything and whisk the ingredients together until the mixture is smooth.
Pour the batter into the prepared pan and bake for 30-35 minutes. Bake for the minimum time if you'd like a fudgier cake texture. The cake is done when it springs back softly when lightly pressed in the center (or you can do the toothpick test, but I rarely do that!)
Remove cake from the oven, place on a wire rack and cool for 5-10 minutes. Run a knife gently along the edge of the cake around the pan, then carefully turn the pan upside down to remove the cake, and leave to completely cool (right side up) before adding frosting.
For the frosting:
While the cake is cooling, place a medium bowl and your whisk into the refrigerator to cool for at least 15 minutes. When ready to frost, remove the bowl, whisk and cream from the refrigerator. Place cream, icing sugar, vanilla and food coloring, if using, in the bowl, and whisk (either with a handheld mixer with whisk attachment, electric whisk, or by hand!) just until stiff peaks firm (any longer and the mixture will start looking grainy and curdled, at which time you'll have to start over with a new cup of cream). Immediately spread the whipped cream onto the cooled cake with an offset spatula, leaving craters and mountains in the whipped cream to give it texture and to collect pools of caramel sauce.
Just before serving, drizzle the caramel sauce over the whipped cream. If needed, briefly warm up the caramel sauce in the microwave to make it easier to pour, but make sure it is room temperature before drizzling it on top of the whipped cream or the whipped cream will melt!
Lastly, pile on that popcorn and dig in!