Preheat oven to 340 F or boil water to prepare the steamer. Also grease a Pyrex 7 cup round container with some oil (spray oil works fine, too).
Microwave heavy cream and almond milk together in a shallow microwave safe bowl, COVERED to avoid splatter - until hot. About 60-90 seconds. (This is an optional step to make the mochi chewier. Read notes**)
Mix the hot cream mixture with brown sugar and pumpkin puree
Add the glutinous rice flour (mochiko flour) and tapioca flour to the wet ingredients and use a whisk to mix until smooth
Add the raisins, diced crystallized ginger and walnuts to the batter
Pour batter into the greased cake pan / pyrex containers, and steam batter for 40-50 minutes for TWO 5.6 inch round cakes (Pyrex 4 cup round glass container), or about 60-70 minutes for ONE 7.25 inch round cakes (Pyrex 7 cup round glass container), or until the center of the mochi cake is set.
Alternatively, you could also bake the rice cakes in the oven - 340F for 40 minutes for TWO 5.6 inch round cakes (Pyrex 4 cup round glass container), or about 60 minutes for ONE 7.25 inch round cakes (Pyrex 7 cup round glass container), or until the middle is set and the edges are crispy.
Let cool completely before serving, or cool the cakes in the freezer for 2-3 hours which helps to get clean slices of cakes.
Fry the sliced mochi cakes in oil if desired. Enjoy!