Preheat oven to 325 degrees F. Lightly butter a 9-inch round foil pan; set aside. In a bowl, stir together flour and baking powder; set aside.
In a medium saucepan, combine the 1/2 cup butter and the unsweetened chocolate. Cook and stir over medium heat until melted and smooth. Remove from heat. Cool slightly (about 5 minutes).
Stir the 1 cup sugar into slightly cooled chocolate mixture in saucepan. Add the eggs one at a time, beating with a wooden spoon after each addition just until combined. Stir in almond extract and vanilla. Add flour mixture; stir just until combined. Spread batter evenly in prepared pan. Bake for 25 minutes. Cool on a wire rack.
For ganache, in a small saucepan, heat whipping cream over medium heat until simmering. Remove from heat; add bittersweet chocolate. Let stand for 5 minutes; stir gently until smooth. Let ganache cool for 15 minutes.
While ganache is cooling, prepare sugared almonds. Butter a sheet of foil; set aside. In a large skillet, combine almonds, the 1/4 cup sugar, the 1 tablespoon butter, and the salt. Cook, without stirring, over medium heat until butter starts to melt. Stir melted butter and almonds together. Continue to cook, without stirring, about 8 minutes or until sugar starts to melt. Stir mixture until almonds are evenly toasted. Spread nuts on buttered foil, separating into small clusters; cool.
Spoon ganache over brownies, spreading evenly. Sprinkle with sugared almonds. Let stand about 30 minutes or until ganache is firm.