In a large bowl, mix the powdered almonds, sugar, lemon zest ans cinnamon.
Add the eggs one by one. Note, the eggs need to be added gently; instead of beating them in, stir until you habe a homogenous batter.
Pour the batter into the greased and floured tin and bake at 170°C for about 40 minutes.
Let the cake cool, then decorate the surface. Cut out a cardboard Saint James cross and place it on top of the cake. Then, using a sifter, cover the cake with icing sugar. remove the cardboard, and your traditional Torta de Santiago is ready to serve.
This is a Galician speciality, most likely derived from medieval almond cakes. As it is made without flour, it is a good gluten-free option.