If you're looking for Ontario-made Parmesan-style cheese, check out Bright Brand Cheese and Butter! They're actually Ontario's oldest Cheddar maker.
Preheat the oven to 350°F (180°C). Lightly grease and line an 8-inch (20 cm) square pan with parchment paper.
Heat a medium sauté pan over medium-high heat and add the oil, followed by the mushrooms and shallot (or onion). Sauté the mushrooms until any liquid has evaporated, about 8 minutes. Stir in the garlic, vermouth and oregano and stir until the vermouth has evaporated. Remove from the heat.
In a large mixing bowl, beat the cream cheese by hand to soften it and then beat in the sour cream (you can switch to a whisk here to make sure it’s smooth.) Stir in the Parmesan, breadcrumbs, eggs, egg yolk, salt, pepper and nutmeg until evenly combined.
Drain the thawed spinach and squeeze out any excess liquid. Add to the cream cheese mixture and stir well, breaking up the spinach to make sure it is well blended (it can be dense after squeezing). Stir in the mushroom mixture and spoon into the prepared pan, spreading to make it level.
Bake for about 30 minutes, until the centre springs back when gently pressed. Cool the squares on a wire rack for at least 20 minutes before slicing to serve. Serve warm or at room temperature.
TIP: These squares are a real timesaver when you make them ahead and then chill or freeze them. Slice them cold (it’s easier to slice them chilled) and then warm on a baking tray at 325 °F (160 °C) for about 12 minutes before serving.