Position rack in center of oven and preheat to 325°F. Line 2 large baking sheets with parchment paper.
Whisk first 7 ingredients in large bowl to blend. Stir brown sugar, butter, and molasses in medium saucepan over low heat until melted. Increase heat to medium-high and bring to boil, stirring constantly.
Remove from heat.
Let cool 10 minutes.
Whisk egg in medium bowl to blend. Gradually whisk molasses mixture into egg. Using electric mixer, gradually beat molasses mixture into flour mixture until just blended.
Roll dough out on lightly floured surface to 12x10-inch rectangle.
Cut out gingerbread with cookie cutters.
Transfer to baking sheets, spacing 1 inch apart. Gather scraps and roll out on lightly floured surface; cut out additional cookies. Repeat until all dough is used.
Bake cookies, 1 sheet at a time, until puffed and tops are firm, about 10 minutes. Cool on sheets 5 minutes.
Transfer to rack; cool completely.
Place rack over rimmed baking sheet. Stir chocolate and oil in top of double boiler set over barely simmering water until melted. Holding bottom of 1 cookie, dip top into chocolate, allowing excess to drip off.
Transfer cookies, chocolate-side up, to prepared rack. Repeat with remaining cookies and chocolate. Decorate cookies with candies or ginger. Chill cookies until chocolate is set, about 30 minutes. (Cookies can be made 3 days ahead. Store in single layer in airtight container in refrigerator.)
Let cookies stand at room temperature 15 minutes before serving.
