1. Position a rack in the middle of the oven and preheat to 350 degrees.

2. Pulse the hazelnuts and ¾ cup of the sugar in a food processor until the nuts are finely ground. Pour into a bowl and stir in the flour.

3. Melt the butter over low heat and continue to cook for a minute or so, until it turns a light golden color. Remove from the heat and let cool, then add the rum and vanilla.

4. In the clean, dry bowl of a heavy-duty mixer fitted with the whisk, beat the egg whites with the salt until they form a very soft peak. Beat in the remaining ¾ cup sugar in a very slow stream, and continue beating until the egg whites hold a soft peak again.

5. Beginning with the hazelnut mixture, alternately fold in the hazelnut and butter mixtures, one-third at a time. Pour the batter into the prepared pan and smooth the top.

6. Bake for about 50 minutes, until the cake is well risen and golden. The center should feel firm when pressed with the palm of your hand.

7. Cool the financier briefly on a rack, then unmold and remove the paper. Turn the cake right side up to finish cooling.

8. Just before serving, dust very lightly with confectioners’ sugar.