Preheat oven to 400 degrees F. Prepare Cornmeal Biscuits. Place on baking sheet; brush with egg and sprinkle lightly with salt. Partially bake about 12 minutes or until lightly golden. Remove from oven. Heat butter and oil in large skillet over medium heat. Add leeks; cook and stir 4 minutes. Stir in mushrooms, garlic, black pepper, and salt. Cook and stir 4 to 6 minutes or until liquid evaporates and mushrooms are just brown.
Stir flour into leek mixture; stir 1 minute. Add broth and cream. Cook and stir until bubbly. Add remaining ingredients; bring to boiling. Transfer to 2-quart baking dish.
Arrange partially baked biscuits on top. Bake 15 to 20 minutes or until biscuits are golden brown and salmon flakes easily.
In a large bowl stir together the flour, cornmeal, baking powder, and salt. Cut in shortening until 8 pea-size. Stir in buttermilk. Turn mixture out onto a floured surface. Knead gently 10 to 15 strokes until dough comes together. Pat to 3/4-inch thickness. Cut into eight 2 1/2-inch rounds, repatting as necessary. Place on casserole as directed in Step 3. Or bake in 400 degrees F oven for 12 to 15 minutes. Makes 8 biscuits.