First of all, make sure that your cookie iron is well washed, cleaned and dried.

Now we are making the dough:

In a bowl, whisk together the sugar and egg.

Add flour, baking powder, vanilla and softened butter.

Mix well with your hands until the flour is incorporated.

Transfer the dough to the floured table and knead a little more to make it uniform.

Break pieces from the dough: shape into a thin log and cut into pieces about 5-7 grams.

I was a little bored of weighing each piece, so I measured them by eye.

The walnuts won't be perfect anyway, they have some sticking-out edges after baking. If the edge is bigger and there is a lot of leftovers, I put them all in the filling.

Heat the iron well. You can grease it with very little oil before the first batch of walnuts (I didn't).

Place the pieces of dough in each shape.

Press well and bake on the stovetop, over medium heat, on one side, then on the other. Insist more on the bulging side, the one with the walnuts.

From time to time, check: open the iron and see if they have browned enough.

This would be the perfect color.

Arrange on a tray or a plate. If they don't come out on their own, help them with the tip of the knife.

If there are any crumbs left, rub the inside of the iron with a dry napkin.

After you've made all the walnuts, let them cool a little.

Then clean the sticking-out edges with a knife, or even rub with your fingers, if the edges are small. The dough is very fragile and crumbles easily.

I got about one hundred walnut shells (meaning fifty whole walnuts), give or take the tastings in the process.

The ones that were too brown were the ones tasted first :)

Now comes the stuffing part.

You can fill them with what you like. The only condition is that the filling is thick and sticky, not runny.

I chose condensed milk. Take a can of condensed milk, place in a pot and bring to the boil. It must be completely covered with water, otherwise it explodes! Let simmer for about three or four hours. If the water level drops in the meantime, add a little more hot water, so that the can is covered at all times.

After it has boiled, let cool completely. Then open the can.

It should be brown-beige and rather thicker. Mine was a bit too liquid, I should have boiled it for another hour, but I mixed it with the nuts and it was good.

Mix the caramel cream with ground walnuts and the leftover biscuits. Adjust everything by eye to obtain a thick and sticky consistency.

Put some filling in a shell, a bit more, to stick out.

And close with an empty shell, without filling.

Test to see if it holds well, if not, add a little more filling.

They are good to eat immediately, but they will be even better if you let them infuse for one or two days. It's the perfect recipe to make them all in advance, the shells and the stuffed walnuts.

Enjoy!