Prepare Jello according to package instructions. As the water is boiling, chill desired serving glasses in the fridge.
Allow Jello to cool to room temperature.
Remove glasses from the fridge. Place glasses so they are resting inside or atop something sturdy at a slight angle (45 degrees). For our stemmed cocktail glasses, we found using a loaf pan worked perfectly. The whiskey glasses rested at the perfect angle along taco trays. You can also create this same angle using foil if all else fails! *Use any glassware desired. We used a mix of cocktail glasses and whiskey glasses. This recipe makes 8 ½ cups of jello, and depending on the size of your glassware each glass will hold between 1to 2 cups of jello. Remove 1 cup of jello and pour into a glass bowl. Add in 1 cup of cool whip and whisk. Refrigerate for 2 hours. (If separation occurs , whisk well and let set for at least 10 minutes after stirring)
Meanwhile, very carefully pour the jello into the glasses until it reaches the rim of the glass. Place into the fridge until the jello is set. (2 hours)
After 2 hours the jello should be set enough to move on to layering. Be gentle as it is still at a fragile stage. Keep the glasses at an angle. Add shortbread cookies to a food processor, (or ziplock bag). Once they reach crumb like texture, scoop 2-3 spoonfuls into each glass over the top of the jello. Gently press down on the crumbs to even the layer. Add more for a thicker layer if desired. *save some for sprinkling on top at the end!*
Next, scoop the jello mixed with cool whip into the glass over the crumbs. It will have a fluffy, slightly dense but pliable texture. Use a spatula to smooth. At this point, you can stand the glasses up straight as the parfait fully sets. (Chill for at least 2 full hours, but if possible, I recommend overnight)
When 1 hour remains on chilling time (or 1 hour prior to serving) Prepare the topping. Combine cool Whip, marshmallow fluff, and sour cream in a bowl and whisk well until smooth. Add a dollop onto the top of each parfait.
When ready to serve, add sliced strawberries and shortbread crumbs on top of the parfait.