Melt 3 TBSP butter in a medium saute pan. Add onions, and cook over medium heat for 3 minutes, stirring frequently. Add mushrooms, and cook over medium heat for 5 minutes, or until lightly browned. Add potatoes, and cook stirring frequently, for an additional 4-5 minutes. Create a hole in the center of the mixture, and add the frozen peas and carrots, and the marsala, water, worchestershire, and vegetable base. Stir, and cook over medium-low heat until the sauce has thickened slightly. If necessary, you can add a small amount of flour/water slurry to tighten it up. I didn't need this. Add seasonings, stir, and set aside.
Prepare your biscuit topping by mixing the flour, baking soda, baking powder, buttermilk powder, and salt in a bowl. Mix in the butter by hand, until the mixture is slightly crumbly. Stir in green onions and basil. Gently mix in the beaten egg and milk. Scoop biscuit mixture out onto a floured surface and knead a few times. Divide dough into 4 equal parts, and taking one part form a small circle that fits on top of your ramekin. Repeat with remaining 3 dough portions.
Prepare ramekins by spraying with cooking spray. Spoon 1/4 of the mushroom mixture into ramekin, and place biscuit disc on top, making sure not to have any overhang. Repeat with remaining mixture and dough. Bake at 400 degrees for 10-15 minutes, or until the biscuits are puffed up and lightly golden brown.