Place 8-10 shot glasses into a 12-cup cupcake baking pan so that the glasses are tipped on their sides. Set aside.
Prepare jelly according to package directions. Transfer jelly to a cup or jug with a pouring spout and carefully pour the jelly into each of the shot glasses. If you find it easier, lift out the shot glass, keeping it sideways, and carefully pour the jelly into the glass while holding it, then gently place it back, sideways, into the cupcake pan. Pour the jelly almost up to the rim of the glass while the glass is on its side.
Refrigerate the jelly for at least 2 hours, or until firm.
Just before you take the jelly out of the refrigerator, prepare the strawberry hearts. Cut the tops off the strawberries and slice the strawberries in half. Place the strawberries cut-side down, and using a small heart-shaped cookie cutter, cut hearts out of the strawberry halves. Set aside.
Pour the thickened cream into a medium bowl. Sift over the powdered sugar and add the vanilla extract. Whisk the cream to stiff peaks (using an electric mixer, or by hand), being careful not to overbeat the cream.
Transfer the whipped cream to a piping bag and cut the tip off (leaving an opening somewhere around medium-sized, but not too big). Pipe a circle of whipped cream around the edge of the jelly, next to the glass (I found that this helps eliminate pockets of air around the top edge of the jelly layer). Then place the piping bag tip in the middle of the circle and squeeze out the whipped cream until it reaches the top of the glass. Feel free to use a star tip, or do some fancy swirls, if you like! You can also just spoon it into the glass, either way will still look great!
When finished piping all of the whipped cream, gently place a strawberry heart in the middle of each mountain of whipped cream. Serve immediately, or refrigerate up to 6 hours, covered.
* You can also use thawed Cool Whip, if preferred, or it's is easier for you.