Whisk together flour, cocoa, baking soda, salt and garam masala.
Combine butter, brown sugar and ginger in work bowl of stand mixer with paddle. Beat until light and fluffy, about 5 minutes. Scrape down sides of bowl, add egg and beat until combined. Add molasses and beat until combined. Add 1/2 dry mixture and beat on low until incorporated; add remaining dry mixture and repeat. Divide dough in half and pat into 1/2" thick rectangles. Wrap in plastic wrap and refrigerate 2-12 hours.
Preheat oven to 350°F Place racks in upper and lower 1/3 of oven. Line 4 baking sheets with parchment or Silpat. Dust a work surface lightly with flour.
Roll out one rectangle to 1/4" thick. Cut with cookie cutters and place cut outs on baking sheets, leaving 1" between cookies. Chill in refrigerator 10 minutes, then transfer to oven to bake until edges are golden, about 12 minutes. Cool on baking sheet 5 minutes then transfer to a rack to cool to room temperature. Decorate with Chocolate Glaze or Royal Icing as desired; top with toasted fennel seeds, dried rose petals or dragees.
For chocolate glaze, combine chocolate, butter, corn syrup and water in a small bowl. Cover with plastic wrap and microwave on high in 30 second bursts, stirring each time, until chocolate melts, about 90 seconds total. Stir until smooth.
For royal icing, combine egg white powder, confectioners' sugar and water in a bowl. Beat with a handheld electric mixer on medium-high until it forms stiff, glossy peaks, about 6 minutes.