Mix butter, lard (both room temperature), lemon peel and powdered sugar with a hand mixer until frothy. Knead in the flour and poppy seeds.
Shape the dough into small walnut-sized balls. Place on a baking sheet and make hollows in the biscuits with your finger. Fill these hollows with plum jam.
Bake in the preheated oven at 175 ° C for about 10 minutes and then dust with powdered sugar and cinnamon.