Preheat the oven to 180C (350F). Brush a 22cm (9in) bundt tin with softened butter and dust with flour shaking out any excess.
Put the butter, sugar and vanilla in the bowl of a stand mixer fitted with the paddle attachment. Beat until light and fluffy, scraping the sides and bottom of the bowl as needed.
Add the eggs, one at a time, and beat until combined. Mix in the orange zest.
Sift all the dry ingredients together in a bowl. Mix the milk, lemon juice and chai together in a measuring jug.
Alternate adding the dry and wet ingredients into the batter, starting and ending with the flour.
Mix in the pumpkin purée until batter is smooth.
Pour the batter into the prepared tin and leve;.
Bake for 50-55 minutes on the lowest oven shelf. The cake is ready when a skewer inserted in the centre comes out clean.
Poke holes into the cake with a long skewer (this is optional) then spoon over the soaking mixture until it gets absorbed into the cake. Do not saturate the cake (you may not need to use it all).
Let the cake cool in the tin. Carefully invert onto a platter, loosening the edges with a knife if necessary.
Mix the icing sugar with enough hot chai tea to reach a pouring consistency. Drizzle the glaze over the cake. Dust with a little ground cinnamon and serve.
Notes
If you can't find canned pumpkin, you can steam or roast a large butternut squash (at least 1kg/2lbs) and then mash it. Cool completely before using.