Heat the oven to 350°F. Grease and flour a springform pan.

Grind the almonds in a food processor until fine.

Cream the butter and sugar with the paddle for 5 minutes until light and fluffy, scraping the sides now and then.

Switch to the whisk. Beat in the eggs and zest until smooth, then the water and the brandy if using. Mix in the flour.

Fold in the almonds with a spatula. Pour the batter into the pan and tap it on the counter to release air bubbles.

Bake about 40 minutes, until a toothpick comes out clean and the center springs back.

Cool 10 minutes, then unmold. Once it's completely cool, dust it generously with powdered sugar.