Preheat the oven to 350°F. Grease a 9-inch round cake pan and dust it with flour.
Steep the tea in the boiling water for 15 minutes, then strain. You should have 1 cup of strong tea.
In a large skillet stir ½ cup sugar over medium high heat until it turns a light caramel color but is still in granules. Do not burn. Gradually add the tea, stirring constantly. When the sugar melts, remove the pan from the heat.
In a large bowl, beat the egg yolks with the remaining 1 cup sugar. Stir in the melted butter and 2 tablespoons jam. Beat in the tea mixture.
Dissolve the baking soda in the vinegar, then stir into the batter. Add the salt and flour and beat well.
Beat the egg whites until soft peaks form; fold them into the batter. Turn the batter into the prepared cake pan and bake until a tester comes out clean, 40 to 45 minutes. Cool the cake in the pan for 10 minutes, then invert onto a rack.
When cool, spread the top with the ½ cup jam and sprinkle the toasted nuts over it.