In a bowl, sprinkle the gelatin over the water. Let bloom for 5 minutes.
In a saucepan off the heat, whisk together the sugar, cornstarch and flour. Whisk in the eggs. Add the milk and sweet clover extract. Bring to a boil over medium heat, whisking constantly and scraping the bottom and sides of the pan. Simmer for 30 seconds.
Off the heat, stir in the gelatin until it dissolves. Strain through a sieve to remove lumps, if needed. Cover with plastic wrap directly on the surface of the cream. Let cool, then refrigerate for 3 hours or until completely chilled. When ready to use, stir with a spatula to soften.
Meanwhile, in a large non-stick skillet over medium-high heat, cook the pears with the brown sugar until they are translucent and caramelized. Deglaze with the water, then bring to a boil. Remove from the heat and let cool. Drain the pears on paper towels.
With the rack in the middle position, preheat the oven to 375°F (190°C). Line a 12 x 17-inch (30 x 43 cm) baking sheet with parchment paper, letting it hang over two sides. Generously butter the paper and the exposed sides of the baking sheet.
In a bowl, combine the flour, baking powder and spices. Set aside.
In another bowl, beat the eggs, brown sugar and molasses with an electric mixer until the mixture triples in volume and forms a ribbon as it falls from the beaters, about 10 minutes. With the mixer at low speed, drizzle in the oil.
Sift the dry ingredients over the egg mixture and gently fold in using a whisk. Spread the batter evenly on the prepared sheet.
Bake for 15 minutes or until a toothpick inserted into the centre of the cake comes out clean. Let cool completely on a wire rack, about 1 hour.
In a bowl, whip the cream with an electric mixer until stiff peaks form. Whisk one-third of the whipped cream into the chilled sweet clover cream until smooth. Using the whisk or a spatula, gently fold in the remaining whipped cream. Cover and refrigerate for 1 hour. Spoon the cream into a pastry bag fitted with a 1/2-inch (1 cm) plain round tip.
Remove the cake from the baking sheet by carefully lifting the parchment paper. Evenly trim the edges of the cake
(see note). Cut into 3 rectangles of different widths: 6 1/2 inches (16.5 cm), 5 inches (12.5 cm) and 4 inches (10 cm).
Place the largest rectangle on a serving platter. Cover with the cream by piping in a tight winding motion, then garnish with the pears. Repeat the sequences with the remaining ingredients, layering the cakes in order from largest to smallest. Refrigerate for at least 3 hours before serving. Decorate with the pears and gingerbread cookies, if desired.
Toast the cake trimmings in the oven to make delicious croutons.