Preheat the oven to 180C / 350F and grease a 3x9-inch pan with oil.
Make the cake: In a mixing bowl, mix together the cake mix, 180 ml of water, sunflower oil and the eggs until combined.
Transfer the batter to the baking pan and bake for 20-25 minutes.
Prepare the jelly: In a saucepan, add 350 ml of water and bring to a boil. Then, turn off the heat, add the strawberry jelly powder and lemon juice, and stir until dissolved.
While that cake is still warm poke holes evenly all over the cake with a skewer (I use a chopstick) and carefully spoon the hot strawberry jelly over the cake, letting it soak in thoroughly. Put the cake in the fridge for at least 4 hours to let the jelly set.
Prepare the topping: In a stand mixer bowl, add the cold heavy cream and honey and whip until a stiff peak forms. Then fold in the sour cream.
Take the cake out of the fridge and spread the cream on top, decorate with strawberry slices and enjoy.
Notes
Keep leftovers in a well-sealed container in the fridge; they’ll stay fresh for 2-3 days!