Follow the directions on the box of jell-o. Reduce your water to 1½ cups instead of two to have your jell-o less watery and stand up better when sliced. Refrigerate overnight.
Day 2 - Make the Cake
For the Joconde Cake
Preheat oven to 450 deg F and grease a jelly roll pan, line with parchment and grease paper.
Using a stand mixer fitted with the paddle attachment, combine the two flours, sugar and eggs. Add the 1 egg yolk and food coloring until desired color is reached.
In a separate, oil free, bowl, whip the egg whites. When foamy, gradually add in the sugar until stiff peaks form. Gently fold the meringue into the almond flour mixture. Add the melted butter and fold again.
Pour mixture into jelly roll pan and bake for 5-8 minutes.
Lay out a tea towel and cover it with ¼ cup of powdered sugar. Remove the cake from the oven and turn out onto tea towel and allow 1 hour to cool.
Remove the base of a spring form pan and use that as a guide to cut out a large circle for the bottom of the cake. Use the sides of the pan to measure the height of the pieces that will be used for the sides. Line the sides with the long strips of cake and then push in the round center piece for the base.
Refer to this post for photos of setting up the cake.
For the Filling
Pour the pineapple juice into a small saucepan and sprinkle powdered gelatin over and allow it to sit for a few minutes until the gelatin has soften. Heat pineapple juice mixture on the stovetop until the gelatin has melted and dissolved.
Remove from heat, stir in the cold water and then pour into a small bowl. Place in refrigerator until mixture has completely cooled (about 5 minutes) but hasn't set up - it should still be liquid.
In a mixer fitted with a whisk attachment, whip the heavy cream and vanilla extract until stiff peaks form. Whisk the pineapple juice mixture into the cream until combined.
Remove Jell-o from the fridge and roughly cut them into 1 inch pieces. I liked them rough and uneven. Set aside 1½ cups of jello cubes to use in the cake.
Pour ¼ of the pineapple cream into the cake mold. Add in a few jello pieces and shake pan to settle the jello. Continue adding cream and jello and shaking the pan until all the cream and jello is in the cake.
If desired, top with whipped cream and smooth top.
Chill the Cake overnight.
Day 3 - Decorating the cake
For the Buttercream Frosting
Mix all ingredients with a paddle attachment and color if desired. Add more/less powdered sugar to get a thick consistency. Add to a piping bag with a Wilton 1M tip and cover the edge of the cake and the cream to form a border. Add sprinkles and sanding sugar to decorate.