Preheat oven to 350º. Grease and flour a 9-inch square pan (my pan was smaller, like 8-inch square and it was fine).
Sift all the dry ingredients into a mixing bowl, add the egg, sugar and molasses. Mix well. It will be crumbly and dry looking. That's okay.
Pour the boiling water and then the oil over the mixture. Start with a wooden spoon, then switch to a whisk, and stir thoroughly until well combined and smooth.
Pour batter into prepared pan, drop on counter a few times to remove air bubbles. Bake on middle rack in oven for 35 to 40 minutes. Cake is done when the top springs back when touched and the edges have started to pull away from the sides of the pan.
While gingerbread is baking, make lemon glaze. Sift powdered sugar into small bowl, add lemon juice and mix well. Set aside.
While the gingerbread is hot, just out of the oven, pour glaze over the top. Set on a rack to cool in the pan.
To make whipped cream, put all the ingredients in a chilled bowl, and with a hand mixer with chilled beaters, beat whipping cream until soft-medium peaks form. Can be prepared 3 hours in advance.
To serve, carefully remove gingerbread to a serving plate. Dust with powdered sugar. Cut square pieces and top with whipped cream.