Preheat oven to 350F. Lightly grease an 8 or 9 inch springform pan and set aside.
In a large mixing bowl whisk together your almond milk, sugar, grapefruit juice, olive oil, vanilla bean paste/extract and grapefruit zest.
Next, sift together your pastry flour, baking soda, baking powder, and salt in a separate mixing bowl. Once evenly mixed, slowly add the dry ingredients to the large mixing bowl until a smooth cake batter is formed.
Add the batter to the greased springform pan. Before putting the pan into the oven, tap the cake pan on the counter to release any large bubbles. Bake for 48 minutes-60 minutes until the cake is browning on top and a toothpick comes out clean when inserted into the middle.
Remove the cake from the oven and let cool to room temperature.
While the cake is cooling, make the glaze by adding the powdered sugar, grapefruit juice, and grapefruit zest to a small bowl and whisking until a thick but smooth glaze forms. If you want a thinner glaze, you can add additional grapefruit juice.
Apply the glaze once the cake has reached room temperature so that it does not melt. Slice into 8 even pieces and enjoy!