To make the cake, in a bowl, stir 1¾ cups of boiling water, dates and bicarbonate of soda. Cover and soak for 4 hours or until dates are very soft.
Position a rack in centre of oven and preheat oven to 175°C (155°C fan-forced). Generously spray a 20cm square baking pan with non-stick cooking spray and line base with baking paper.
In another bowl, whisk flour, baking powder and salt. In a large bowl, using a handheld electric mixer, beat sugar and butter, scraping sides as needed, for about 3 mins or until fluffy. Add eggs, 1 at a time, beating well after each addition. Add vanilla and mix for about 1 min, or until mixture lightens in colour. Reduce speed to low and gradually mix in flour mixture and then date mixture, scraping bowl as needed.
Pour the batter into the prepared dish. Bake, without moving, for about 1 hour 5 mins or until cake springs back when gently pressed and a toothpick inserted into centre of cake comes out with a few moist crumbs attached. Transfer to a rack and cool for 30 mins.
Run a knife around edges to loosen cake. Invert cake onto rack and remove baking paper. Cool cake upside down on rack (this will help level it out).
To make the vanilla toffee frosting, using a paring knife, scrape seeds from vanilla beans and place seeds in a large bowl with cream cheese, butter, sugar, and salt. Using an electric handheld mixer, beat on medium speed for about 6 mins or until smooth and fluffy.
Halve cake horizontally into 2 even layers. Dab some frosting on a cake plate and centre 1 cake layer, cut-side up, on frosting. Brush away any loose crumbs from cake. Using an offset spatula or palette knife, spread 1½ cups of frosting over cake to form a smooth even layer. Top with other cake layer, cut-side down. Press firmly to adhere layers. Spread 2 cups of frosting over top and sides of cake to form a smooth thin layer. Refrigerate cake for about 30 mins or until frosting is not tacky.
Spread the remaining frosting decoratively all over the cake to form a smooth coat. Refrigerate for 30 mins or until frosting is firm.