If your dates have seeds, remove them by slicing each date lengthwise with a paring knife and gently pulling out the pit. Finely chop the pitted dates into small pieces for a smooth mixture later. Set aside.
In a large saucepan, combine the chopped dates and hot water. Bring to a boil over medium heat. Once boiling, add the baking soda—it will bubble and froth, which is normal! Stir well using a spatula, reduce the heat to low, and let the mixture simmer for 5–7 minutes until it breaks down and thickens into a date paste. Allow it to cool for at least 10 minutes before using. (Tip: Cooling prevents the hot mixture from cooking the eggs in the batter.)
Preheat your oven to 175°C (350°F). Line the base of a 10-inch cake pan with parchment paper and butter the sides to prevent sticking. In a medium bowl, whisk together the flour, baking powder, and cardamom. In a large mixing bowl, cream the butter and brown sugar with an electric mixer until light and fluffy. Add the eggs one at a time, mixing well after each addition. Add the dry ingredients to the creamed butter and sugar mixture, mixing on low speed with an electric mixer until just combined. Then, add the date puree and continue mixing until the batter is smooth and fully incorporated.
Pour the batter into the prepared pan and smooth the surface with an offset spatula. Bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean. Avoid overbaking to keep the cake moist and gooey. Let the cake cool in the pan for 30 minutes.
Flip the cake out of the pan, peel off the parchment paper, and transfer it to a wire rack to cool completely.
Slice the cake and serve warm with my crème anglaise, vanilla ice cream, clotted cream, whipped cream, or a drizzle of caramel sauce.