Preheat your oven to 400˚F. Grab two mixing bowls and one cereal bowl.
In the first mixing bowl, we’re making cake batter. Whisk together flour, sugar, baking powder, salt, cardamom.
Add the cold butter pieces to the cake batter bowl and use your hands to mix the butter into the flour, squishing the butter in between your fingers and making little buttery flour crumbs. Work fast—can’t let the butter melt.
In the cereal bowl, whisk milk and egg well. Pour the milk mixture over the cake batter mixture. Mix lightly with a fork there are no more flour streaks (it will be on the dry side).
Take a stick of butter and grease your spring form pan. Spread the cake batter on the bottom of the pan with le rubber spatula.
Arrange your pretty sliced peaches and berries on top of the cake batter. Bake this in the oven for no more than 15 min or until just golden on top. Underbaking is preferred here because this has to bake again later!
While the cake layer is in the oven, get started on the custard layer. In your second mixing bowl, whisk together 1/4 cups of heavy cream with the flour. This will make a smooth base for the rest of the custard.
Now you can whisk in the rest of the heavy cream, sugar, egg, vanilla, and salt.
Is that cake layer done? Take it out of the oven and place it on top of a long sheet of aluminum foil. Fold the foil up around the sides to encase the pan.
Pour the custard mix on top of the cake. Yes, that’s right. ON TOP of the baked cake layer!
Put the whole thing, foil and all, back in the oven. and reduce the heat to 350˚F. Continue to bake for 35-40 minutes.
Keep checking the oven near the end of the process, your cake will be ready to exit the oven when it is caramel-y golden brown.
While the cake cools, make your cream sauce in less than a minute: just mix all the condensed milk, heavy cream, milk, and vanilla together.
When your cake is cooled (after 20 minutes), release from the springform pan and cut a slice. Spoon some cream sauce on a bowl or plate and plop that custard cake on top. The end.