Combine together flour, custard powder, baking soda and baking powder and sift it. Keep it aside. Add brown sugar to softened butter and combine well using a whisk. Add oil and whisk. Make sure its mixed well. Add honey and vanilla essence and whisk again. Add eggs, one at a time, whisking after each addition. Make sure that you get a lump free batter.
Add the sifted flour mixture, little by little, to the egg mixture. Whisk well after each addition. Pour the prepared batter to a well greased steaming dish. Cover the dish with aluminium foil. Place the dish in a steamer/appachembu filled with water. Steam for 35 - 45 mins (refer notes). Allow the cake to cool in the tin for 10 - 15 mins and remove from pan. Serve with vanilla ice cream and drizzled honey.
Notes
I steamed it in low - medium flame. After the first 25 minutes, check the water level and add more water, if required. The cake should be done in 35 - 40 mins, ideally. So check it at around that time. I made the cake in a 6 inch round aluminium tin. You can store the cake at room temperature upto 3 days and can be stored in the refrigerator upto 5 days. If kept in refrigerator, microwave it for 10-15 seconds before serving.