Preheat your oven to 400°F (204°C). Dice the mushrooms, onions, and tomatoes if using. Mince the garlic and measure out all remaining ingredients. Having everything ready makes the cooking process much smoother.
Place the sausage in a large oven-safe skillet over medium-high heat. Break it apart while cooking and add the diced onion once some fat has rendered. Continue cooking until the sausage is fully browned and the onions are soft and translucent.
Remove the sausage mixture and set it aside. Add olive oil and butter to the same skillet. Stir in the mushrooms and cook until they soften and release their moisture, allowing much of the liquid to evaporate.
Sprinkle in the thyme, garlic, salt, and pepper. Stir continuously for about one minute. This short cooking time allows the garlic and herbs to become fragrant without burning.
Add the cream cheese cubes directly to the skillet. Stir until completely melted and smooth. Pour in the half-and-half and add the grated cheese blend, stirring until everything becomes creamy and well combined.
Return the cooked sausage and onion mixture to the skillet. Mix thoroughly so every bite contains mushrooms, sausage, and cheese. If using cherry tomatoes, fold them in gently at this stage.
In a small bowl, combine the panko breadcrumbs with melted butter. Mix until the breadcrumbs are evenly coated. Sprinkle the mixture evenly over the top of the dip.
Transfer the skillet to the oven and bake for 15–25 minutes. The dip should be bubbling around the edges, and the breadcrumb topping should be golden brown and crisp.
Allow the dip to rest for about 5 minutes after baking. This helps the cheese set slightly and makes serving easier. Serve warm with your favorite dippers.