1. Coat 9-inch springform pan with nonstick cooking spray.
2. Combine chocolate and butter in large glass bowl. Microwave on high power for 1 minute until melted; stir until smooth. If needed, microwave another 30 seconds to 1 minute, then stir. Let cool slightly.
3. Meanwhile, heat oven to 375 degrees F. Knead together almond paste and the 3 tablespoons confectioners sugar on flat work surface. Roll out into 8-inch circle.
4. Beat granulated sugar into chocolate mixture until smooth, about 1 minute. Add eggs, one at a time, beating after each until blended; beat on high speed until slightly airy, about 2 minutes. Beat in vanilla and salt until blended. Sift the cocoa powder over the top of chocolate mixture; beat on low speed until blended, about 1 minute. Pour half the batter into prepared pan. Carefully fit the almond paste round on top of the batter in the pan. Scrape remaining chocolate batter into pan; spread to cover the round and smooth the top. Gently arrange whole almonds on top of batter.
5. Bake in 375 degrees F oven for 30 minutes. Remove the pan to wire rack and let cool to room temperature. Then refrigerate for 2 hours. Remove side of pan. Sprinkle the top with the 1 tablespoon confectioners sugar. Slice and serve.