In a medium bowl mix dry ingredients: flour, sugar, baking powder and salt.
In the large bowl of an electric mixer, whisk softened butter on medium speed for 1-2 minutes.
Add dry ingredients and combine with butter for 30-40 seconds.
Add heavy cream, oil, clementine zest, vanilla bean seeds and eggs one at a time, mix on medium-high for one minute.
Pour batter into prepared pans. Bake for 20-25 minutes, a tooth stick inserted into the center of the cake must come clean.
Add clementine juice to a medium sauce pan and sprinkle the gelatin over it. Let it sit for 1-2 minutes. Turn the stove on, and on low heat stir in the sugar into the juice and gelatin mixture. Cook stirring for 3-5 minutes, just until all the sugar and gelatin has dissolved.
Transfer the mixture to a glass bowl and refrigerate for 30-40 minutes, or just until settled. Its important to check on the mixture every 5 minutes after 30 minutes have passed and give it a few stirs. The mixture is ready when it has a pudding texture.
Whisk the heavy whipping cream on high speed until stiff, when soft peaks have been formed, reduce the mixer speed to low and add the gelatin mixture to it. Whisk on low until combined. Make sure to scrape the walls of the bowl with a spatula, to make sure the mixture is fully combined.
Place the yellow cake into the center of a 9 inch springform pan, there will be space around it. Pour the mousse over the cake letting it fill in around the side. Refrigerate at least for 1 hour before adding the peach jelly layer.
NOTE: if you have a higher springform pan, or a cake ring, pour some of the mousse over the cake, top it with the second layer, and cover with the remaining mousse mixture.
Follow instructions on the box on how to prepare the jelly. Let the jelly cool to almost room temperature, I usually give the bowl an ice bath to speed up the process. Watch the jelly closely, and stir it often, to make sure it doesn't fully settle. After the ice bath, when the jelly temperature has reached almost room temperature, pour it over the mousse.
Refrigerate for at least 4-6 hours before serving the cake. Remove cake from the fridge and run knife around inside rim of pan to loosen cake; remove side of pan, slice and serve.