Prep: Preheat the oven to 350°F. Grease the bottom of a 9x13" baking pan and set aside.
Dry ingredients: In a medium mixing bowl, stir together the flour, pumpkin pie spice, baking powder, baking soda, and salt. Set aside.
Cream butter and sugars: In a large mixing bowl, add the softened butter. Use an electric hand mixer to beat the butter until creamy and pale in colour. Add the brown sugar and molasses and beat together until fluffy.
Beat in eggs: Beat in one egg at a time, mixing well in between each addition. Add the pumpkin puree and vanilla extract and mix until combined.
Mix batter: Add half of the flour mixture and mix on low speed until just combined. Add all of the milk and mix until mostly combined. Finish with mixing in the remaining flour mixture until just combined.
Fill pan: Pour the batter into a 9x13" baking pan. Use an offset spatula to smooth the batter into an even layer and into the corners of the pan.
Bake: Bake for 40-45 minutes or until a toothpick inserted in the middle comes out mostly clean.
Toffee Sauce
Tip: While the cake is baking, prepare the toffee sauce so that it's ready to use once the cake comes out of the oven.
Cook sauce: In a small saucepan, add the butter, brown sugar, heavy cream, vanilla extract, and salt. Bring it to a boil on medium-high heat and then turn it down to medium and let it simmer for about 2 minutes for a thinner sauce or 5 minutes for a thicker sauce, stirring often.
Soak cake in toffee sauce: Immediately after taking the cake out of the oven, use a chopstick to poke holes across the entire cake. Pour most of the toffee sauce on top of the cake, reserving some for serving. Use an offset spatula to spread the sauce across the cake.
Slice: Slice and serve while warm with a scoop of ice cream and extra toffee sauce.
Notes
Pumpkin pie spice: You can use store-bought pumpkin pie spice mix or make your own. To make your own, stir together:
2 teaspoon ground cinnamon
1 teaspoon ground ginger
1 teaspoon ground nutmeg
½ teaspoon ground cardamom
½ teaspoon ground cloves
You can double or triple this mix as needed. Use what you need from this mixture and save the rest for other recipes!