Pour boiling water over dates in a bowl, add baking soda, cover, and soak for 20 minutes.
Preheat the oven to 350°F. Grease 2 ramekins generously with butter.
Blend dates and water into a paste.
In a separate bowl, whisk butter, sugar, and vanilla until light and fluffy.
Add egg yolk and whisk to combine.
Fold in the date paste.
Sift in flour, baking powder, cinnamon, and salt. Gently fold to combine.
Divide batter between ramekins, spreading evenly.
Bake for ~25 minutes or until a toothpick comes out with moist crumbs attached.