Step 1: Preheat your oven to 350°F (175°C). Grease and flour your Bundt pan generously.
Step 2: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
Step 3: In a large mixing bowl, beat the softened butter and granulated sugar together until light and fluffy, about 3-5 minutes.
Step 4: Add the egg whites and whole eggs one at a time, mixing well after each addition.
Step 5: Pour in the buttermilk, almond extract, and vanilla extract. Mix until well combined.
Step 6: Gradually add the dry mixture to the wet ingredients, mixing on low speed until just combined.
Step 7: Carefully pour the batter into the prepared Bundt pan, smoothing the top with a spatula.
Step 8: Bake for 50-60 minutes, or until a toothpick inserted comes out clean.
Step 9: Let the cake cool in the pan for about 10 minutes, then invert it onto a cooling rack.
Step 10: In a small bowl, whisk together the powdered sugar, milk, and almond extract until smooth.
Step 11: Drizzle the glaze over the cooled cake and sprinkle with slivered almonds.