Preheat oven to 325 degrees. Butter an 8-inch square pan, and line it with parchment, leaving a 2-inch overhang on 2 sides. Butter and flour parchment, tapping out excess.
Combine flour and salt in a small bowl. Melt butter in a medium saucepan over medium heat. Sift cocoa powder on top of butter, and whisk to combine. Let cool 3 minutes. Gently whisk in vanilla and eggs, then stir in sugars and flour mixture until just combined. Fold in almonds, then spread batter evenly in prepared pan.
Bake until the top is firm and set, about 30 minutes. Transfer pan to a wire rack, and let cool for 20 minutes. Remove brownies from pan using parchment overhang, and let cool on wire rack. (Brownies will keep at room temperature for up to 3 days.)
Using the large coffin template, cut out brownies. Dust marzipan lightly with cocoa powder, and mix until marbled dark brown. Roll out marzipan to 1/4-inch thickness. Using the small coffin template, cut out 1 marzipan coffin for each brownie. Gently press a coffin on top of each brownie.
Fill a pastry bag fitted with the smallest plain round tip with royal icing. Decorate marzipan with small dots around the edges, and apply 1 fleur-de-lis to each coffin with a small offset spatula, securing each with a dot of royal icing.