Preheat the oven to 350 degrees Fahrenheit (177 degrees Celsius) and grease a 9-inch by 9-inch square cake pan.
Whisk the tomato soup and soda together in a small bowl, then set aside.
Cream the butter and sugar together in a bowl until light and fluffy, then add the egg and mix until combined.
Pour in the tomato soup and beat together, then sift in the flour, salt, cinnamon, nutmeg and ginger and combine.
Stir in the raisins then pour into a greased 9" x 9" square cake pan.
Bake for about 30 - 35 minutes or until a toothpick test comes out clean - do not overbake.
While the cake cools, make the icing.
for the icing:
Melt the butter in a heavy, medium sized sauce pan.
Stir in the brown sugar, condensed milk, vanilla and sea salt. Let the mixture come to a boil, stirring constantly and allow it to boil for about 6 - 10 minutes.
Remove from heat and let it cool slightly, then pour over the cake while still a bit warm and spread evenly then allow to cool completely before serving.
Recipe Notes
Don't overmix or undermix the cake batter lest you want to end up with a chewy, dense cake. Don't overmix the frosting either; it'll become runny.
Give your cake about 1-2 hours to cool before frosting. A cooled cake is so much easier to work with.
It's best to wait for all refrigerated ingredients to come to room temperature for the best results.
You're welcome to sub the raisins with pecans, chopped walnuts, or currants.
If you don't have nutmeg and cinnamon, simply use spice cake mix or ground allspice.
For a more intense and warm flavor, toss half a teaspoon of ground cloves in the batter. For the icing, you can add a dash of pumpkin spice or cinnamon.
Instead of the cake pan, feel free to use a tube pan, bundt pan, or loaf pan. But keep an eye on the oven to ensure proper doneness.
If you don't have baking soda on hand, replace it with 3× baking powder and half the salt amount. This means 3 teaspoons baking powder and ¼ teaspoon salt.