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1
Preheat oven to 350 degrees with oven rack in upper-middle position.
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2
Melt 2 tablespoons of the butter in a medium saucepan over medium-low heat.
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3
Add chopped onion and 1/2 tsp salt; cook until translucent, about 5 minutes.
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4
Add garlic and thyme and cook until fragrant, about 30 seconds.
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5
Add broth, increase heat to medium-high, and bring to a boil.
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6
Cover and remove from heat.
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7
Pulse bread, Parmesan, remaining 2 tablespoons butter, 1/2 tsp salt and 1/2 tsp pepper in food processor until coarsely ground, 8 to 10 pulses; transfer to bowl and set aside.
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8
Combine spinach, cream cheese, 1/2 tsp salt, and 1/4 tsp pepper in the now-empty food processor bowl and process until smooth, about 10 seconds.
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9
Spread spinach mixture in even layer in 13 by 9 inch baking dish.
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10
Sprinkle rice evenly over spinach mixture.
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11
Sprinkle cheddar cheese over rice.
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12
Pour broth mixture into baking dish, cover tightly with double layer of aluminum foil, and bake for 25 minutes.
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13
Remove casserole from oven, remove foil and stir to redistribute ingredients.
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14
Return casserole to oven, increase temperature to 450 degrees, and continue baking, uncovered, until all the liquid is absorbed, about 15 minutes.
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15
Sprinkle bread-crumb mixture over top and bake until golden brown, about 8 to 10 minutes.
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16
Let casserole cool for 20 minutes before serving.
