Step 1

Preheat oven to 400ºF. Coat a 2 ½ quart baking dish with cooking spray.

Step 2

Heat 1 tablespoon oil in a large non-stick skillet over medium-high heat. Add chicken and cook, stirring once or twice, until browned on the outside and just cooked through, 7 to 10 minutes. Transfer to a plate and tent with foil.

Step 3

Return the skillet to medium heat and add 2 teaspoons oil. Add onion, garlic, salt, pepper and thyme and cook, stirring often until the onion is softened and starting to brown slightly, 3 to 4 minutes. Add sherry, increase heat to high and simmer, scraping up any browned bits (or until the sherry is almost completely evaporated), 1 to 3 minutes.

Step 4

Stir in 1 ½ cups broth and bring to a simmer, stirring occasionally. Stir the remaining ½ cup broth and flour in a small bowl to make a slurry. Gradually whisk the slurry into the simmering vegetable mixture. Bring to a simmer, stirring constantly. The sauce will thicken when it reaches the simmering point.

Step 5

Remove the skillet from the heat. Stir in 1/3 cup parmesan and sour cream. Stir in the chicken and any accumulated juices.

Step 6

Meanwhile, place broccoli and ½ cup water in a microwave-safe bowl. Cover with a layer of parchment and then a layer of plastic wrap and microwave until the broccoli is bright green, about 2 minutes. Carefully remove cover, drain broccoli.

Step 7

Add the broccoli to the chicken mixture. Mix thoroughly. Transfer the mixture to the prepared baking dish.

Step 8

Top with the remaining 1/3 cup Parmesan. Mix the remaining 1 teaspoon oil with panko and paprika in a small dish. Sprinkle over the casserole. Bake until hot all the way through and the top is golden, 15 to 22 minutes.