Preheat the oven to 375°F. Remove the stems from the mushrooms. Finely chop enough stems to yield 1/2 cup and set aside (discard the rest). Lightly brush the mushroom caps with oil. Place the caps, rounded-side down, on a baking sheet lined with parchment paper. Set aside.

To make the stuffing: Melt the butter in a medium nonstick skillet over medium-high heat. Add the onion and cook, stirring occasionally, until fragrant, about 1 minute. Add the mushroom stems and garlic; continue cooking, stirring occasionally, until the mushrooms and onion are tender, about 4 minutes.

Remove the pan from the heat. Stir in all the remaining stuffing ingredients. Taste and adjust the seasoning.

To serve, fill the mushroom caps with the stuffing; sprinkle with paprika. Bake for about 10 minutes, or until the stuffing is heated through and lightly browned. Serve immediately.

*Tip Refrigerate mushrooms for up to 4 days in a paper bag, an open plastic bag, or a basket so air can circulate around them. Do not clean prior to storage; before using, simply brush with a mushroom brush or wipe with a moist paper towel. If it is necessary to rinse them, do so quickly; because mushrooms are very absorbent, they should not be allowed to soak in water. Before using, cut any woody ends from the bottoms of the tender stems. Mushrooms should be cooked quickly; they are 90 percent water, and overcooking results in a mushy texture.

ADVANCE PREPARATION The stuffing can be made up to 1 day in advance; cover and refrigerate. The mushrooms can be stuffed Up to 2 hours before baking; cover and refrigerate. Bring to room temperature before baking.