Preheat oven to 375°F (190°C).

Bake potatoes until tender, about 45 minutes to 1 hour.

While potatoes are baking, cook broccoli according to package directions. Drain well.

Once potatoes are cool enough to handle, halve lengthwise, leaving a 1/4-inch thick shell.

Scoop out the potato flesh into a large bowl.

Add milk and butter to the bowl with the potato flesh and mash until smooth.

Season with salt and pepper.

Spoon the mashed potato mixture back into the potato shells.

In a separate bowl, mix the cooked broccoli, cheese sauce, chopped onion, salt, and pepper until well blended.

Spoon approximately 1/4 cup of the broccoli-cheese mixture onto each potato half.

Place the stuffed potatoes on a baking sheet.

Bake for an additional 10-15 minutes, or until heated through and lightly browned.