Lightly spray 2 8 or 9 inch nonstick cake pans and line with circles of parchment paper at the bottom.
Whisk the eggs in a large mixing bowl. Blend in the oil, buttermilk, and vanilla. Then whisk in the cake mix, mixing until everything is combined and there are no large lumps...small lumps are fine.
Turn the batter into the cake pans. Bake 8 inch pans for 26-31 minutes, and 9 inch pans for 23-28 minutes, or according to your box instructions. The cakes will feel firm to the touch and a toothpick inserted in the center will come out dry. Check them on the earliest time.
Let the cakes cool for 15 minutes on a rack, then turn them out of the pans and let them cool completely on the rack.
Meanwhile whip the cream and confectioner's sugar until it holds stiff peaks.
When the cake is cooled, place one layer flat side up and spread with a thick layer of jam. Spread the whipped cream on top of the jam, and then place the second cake layer on top of that, flat side DOWN. Sprinkle with confectioner's sugar just before serving.