For the polenta cake:
Bring water and milk to a boil. Whisk in polenta, turn down heat to low and stir often with wooden spoon, cooking until polenta is soft, approximately 20 minutes. Look for polenta to firm up and start coming away from the sides of the saucepan. When desired texture is reached, remove saucepan from heat and fold in lemon zest, Parmesan, and thyme. On a cookie sheet evenly spread out polenta mixture to 3/4-inch thickness and place in refrigerator to cool. Remove polenta from the refrigerator and cut out cakes of about 4-inch circumference.**
For the salmon:
Place small amount of oil in a large cast iron or heavy-bottomed pan on high heat. Sear both sides of salmon being careful not to cook beyond medium for best results.
For the vegetables:
Saute pattypan squash and zucchini in saute pan with shallots and extra-virgin olive oil. Do not overcook, leaving a nice crunch to the vegetable
For the sauce:
Make the sauce by browning butter over medium heat until light brown. Add shallots, thyme, sherry vinegar and reduce by a quarter. Add demi-glace and bring to a quick boil. Remove and finish with tomato concasse.
Sear both sides of the polenta cakes over medium heat, allowing them to warm through, as well as, achieve a golden crust. Serve with vegetables and salmon pouring the sauce over the salmon.
*peeled and seeded tomatoes cut into small cubes
**a ring mold or a non-rolled rim glass works great