Mix cake mix according to package directions. Add the lemon zest and tint to a nice, bright yellow with the food coloring. Bake according to package directions. Cool cakes completely.
To assemble jars, crumble cake into large pieces. Fill the bottom 1/2 of the jar with cake. Top with a thin layer of frosting. Add a second layer of crumbled cake on top of that, then finish off your jars with a final layer of frosting. Add sprinkles, if desired.
Twist caps onto the top of your jars. Store at room temperature for up to 24 hours, and in the fridge for up to three days. Because you aren’t sealing the cakes into the jars, this treat is best when not mailed via snail mail.
Makes 3 medium-sized cakes-in-jars (shown in picture) or 6 small, cupcake-sized cakes-in-jars.