Prepare Oven and Pan: Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
Combine Dry Ingredients: In a large bowl, sift together the all-purpose flour, ground almonds, granulated sugar, baking powder, baking soda, and salt.
Mix Wet Ingredients: In another bowl, whisk together the vegetable oil, almond milk, vanilla extract, and apple cider vinegar.
Combine Mixtures: Add the wet ingredients to the dry ingredients and mix until just combined. Gently fold in the chopped rhubarb.
Bake the Cake: Pour the batter into the prepared cake pan. Smooth the top with a spatula.
Bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
Prepare the Glaze: While the cake cools, whisk together powdered sugar, almond milk, and almond extract in a small bowl until smooth. Adjust the thickness by adding more almond milk or powdered sugar as needed.
Cool and Glaze: Let the cake cool completely in the pan on a wire rack. Once cool, invert onto a serving plate.
Drizzle the almond glaze over the top of the cake.
Garnish and Serve: Arrange thin slices of rhubarb and sprinkle toasted almond flakes over the glazed cake.
Let the glaze set before slicing and serving.