Put the puree in a bowl. Add the sugar and beat. Add the oil and the baking soda, dissolved in the vinegar.
Sift the flour, add it to the pumpkin mixture, beating with a mixer at first, then with a whisk. Add the walnuts and cinnamon. Stir well with a spatula.
Lay out a tray with baking paper. Shape balls with moist hands and arrange them in it, with space in between them.
Mix the sugar and cinnamon in a bowl. Sprinkle the cookies with it, place 1/2 a walnut onto each. Bake in a preheated 356°F (180 °C) oven about 15-17 min. Take them out and arrange onto a cooking grid to cool.
The number of cookies depends on the size of the balls you make. I made 25 medium-sized cookies to bake them all at once - you can make even smaller ones.
They're uniquely delicious, perfect for the Nativity Fast or Christmas Eve, for whenever you want to eat something sweet but a little different than the traditional pumpkin pie and stuffed pumpkin.