Combine raisins and whisky in a small bowl. Cover with plastic, and let sit, at room temperature, for at least 4 hours and up to overnight.
Heat oven to 350 degrees. Butter one 12-inch or two 8-inch cake pans; line bottoms with parchment. Butter parchment, and dust pans with flour, making sure to coat pans evenly. Tap out excess flour.
In the top of a double boiler set over simmering water, melt chocolate with 1/4 cup water. Add butter a little at a time, stirring until mixture is smooth.
In a large bowl, beat egg yolks with sugar until thick and light. Stir in melted chocolate mixture. Add flour, almonds, raisins, and whisky. Stir to combine.
Beat egg whites with salt until stiff, glossy peaks form. Stir one-third of egg whites into chocolate mixture. Gently but thoroughly fold in remaining egg whites. Pour into prepared pans, and smooth top. Bake until just beginning to pull away from sides of pan (the center should remain moist), about 25 minutes. Cool cake in pan 10 minutes. Remove cake from pan; transfer to a wire rack to cool completely.
Place cake on a baking sheet lined with a cooling rack. With an offset spatula, spread an even layer of the thicker ganache over entire cake. Still using the offset spatula, pour remaining half of ganache over cake until completely covered and smooth. Garnish with edible flowers.