• Oil a 8 x 8 inch square baking pan and line it with parchment paper overhanging on the sides. If you want to double the recipe, use a 9 x 13 inch pan instead
• Preheat the oven to 350 F (180 C) for conventional oven, 330 F (165 C) for convection oven

Prepare the cake batter:

• Combine all the dry ingredients, except for the walnuts, in a mixing bowl and set aside
• In a large mixing bowl, combine pumpkin puree, grated ginger, molasses, sugar, vanilla extract, and oil. Whisk vigorously for about 30 seconds or so.
  
• Add the eggs and whisk again until the whole mixture is emulsified.
  
• The oil shouldn't separate anymore after this
  
• Add the dry ingredients and walnuts and use a spatula to fold the ingredients.
  
• Do not overmix, but you also want to make sure the dry and the wet ingredients are folded together and you shouldn't see any traces of flour
  
• Scrape the cake batter into the prepared pan. Smooth the top to make sure the cake is level
  

Bake:

• Place the pan on the middle rack in the preheated oven and bake for 30 minutes or until a cake tester inserted into the center of the cake comes out clean

Prepare the toffee sauce:

• While the cake is baking, prepare the toffee sauce. Combine butter, brown sugar, and water in a saucepan. Bring to a boil over medium-high heat. Stir until the butter melts and the sugar dissolves. Continue to cook until the mixture thickened slightly, about 3 minutes
  
• Remove the saucepan from the stove and slowly stream in the heavy cream. It may sputter a bit.
  
• Keep stirring until the mixture is smooth.
  
• Put it back on the stove and cook again over medium-high heat until the toffee is thickened, another 3 minutes. Remove from the stove and stir in the salt. Set aside
  

Pour the sauce over the cake:

• Remove the cake from the oven and set on a cooling rack. Use a skewer or a toothpick to poke deep holes all over the surface of the hot cake.
  
• Pour 1/2 cup of the warm toffee sauce over the entire surface of the cake.
  
• Let the cake sit until it absorbs some of the toffee sauce. The sauce will hardened slightly as it cools down
  

Serve:

• This cake is best served warm. Cut the cake into 9 servings, 3 x 3 grid (or 12 if you want smaller pieces)
• Place one piece on a serving plate. Pour the warm toffee sauce over the cake and serve