Preheat the oven, grease a round cake pan lightly, line the base with baking paper, and prepare all ingredients at room temperature before mixing begins.
Grind the almonds with half the sugar until finely textured, taking care not to process so long that the natural oils create a heavy paste.
Beat the eggs with the remaining sugar until very pale, thick, and airy, then gently fold in the almond mixture without noticeably deflating the batter.
Sift the flour and baking powder over the bowl, add orange zest, and fold carefully with a spatula until no visible dry streaks remain inside.
Pour the batter into the prepared pan, level the surface gently, and bake until golden and a skewer inserted into the exact center emerges clean.
Cool the cake in its pan briefly, then transfer it to a wire rack and allow it to reach full room temperature before decorating completely.
Place the cooled cake on a serving plate, dust generously with powdered sugar, slice with a sharp knife, and serve immediately with tea or coffee.
