Pat your chicken strips completely dry with paper towels — this is key for getting that golden sear. Season both sides with salt and pepper. Heat your skillet over medium-high heat and add the olive oil. Once it's shimmering, you're ready to go.
Working in batches so you don't crowd the pan, sear the chicken for 3-4 minutes per side until golden brown. Don't move it around too much or you'll mess up that beautiful crust. Transfer to a plate and set aside.
In the same skillet, add the butter and sliced mushrooms. You'll hear it sizzle right away — that's exactly what you want. Cook for about 4 minutes, stirring occasionally, until the mushrooms release their moisture and start to soften.
Add your minced garlic and sliced onion to the mushrooms. Stir everything together and cook for another 2 minutes until it gets fragrant. Sprinkle the flour over top and stir it all together, coating everything lightly.
Pour in the chicken broth, white grape juice, and balsamic vinegar. Stir to combine and scrape up any browned bits stuck to the bottom — that's where all the flavor lives. Let this simmer for about 3 minutes.
Stir in the heavy cream and dried thyme, then return the chicken to the skillet. When your kitchen smells like rich, caramelized garlic and cream, you'll know it's almost done. Let everything warm through for 2-3 minutes until the sauce coats the chicken beautifully.
Taste and adjust your seasonings if needed — add more salt, pepper, or a squeeze of lemon if you want brightness. Finish with fresh parsley right before serving. This whole chicken Marsala recipe comes together faster than you'd think.