Gloaters gonna gloat!
It is entirely possible that Aunt Jenny poisoned Calvin and posed him just so, ever to remain in the posture of Spry-induced delight. He doesnt really seem to be looking at the shortcake.
Doesnt this seem like a lot of shortcake for two people? Perhaps old Cal has a wooden leg, or one of those flinty-farmer metabolisms that lets him shovel back the shortcake by the bushel, and never gain a lick of weight. In any case, his delight seems . . . alarming; surely Jenny whips up one of these things every other day. And if its not this, its a pie. Or a cake. Maybe she doesnt make shortcake but once a year, just to keep the occasion special. Calvin lives in a state of perpetual hopefulness - like the end of the world, he knows not the date nor the time of the reappearance of shortcake. Hence his expression of untrammeled joy makes perfect sense. And you said you lost the recipe! Uh, receipt! Why, Jenny: you sly fox, you.