Portobello Herb Butter Pork Sirloin Roast (Slow Cooker) Tips, FAQ & printable recipe

Tips for success

For the most flavorful result, use a good-quality salted butter — the salt enhances the pork and mushrooms beautifully.

If you prefer a thicker sauce, you can mix a tablespoon of cornstarch with a little cold water and stir it into the juices after shredding, then let it simmer for a few minutes. But honestly, the natural jus is perfect as-is, and it soaks into mashed potatoes or bread wonderfully.

Don't be afraid to let the pork cook longer than the minimum time. The slow cooker keeps it moist, and the extra time only makes it more tender.

If you're cooking on high, check at the 4-hour mark — some slow cookers run hotter than others. The key is to look for that fork-tender texture, not just the clock.

Variations

• Add Fresh Herbs: Sprinkle 2 teaspoons of fresh thyme leaves or 1 tablespoon of chopped rosemary over the roast before adding the butter. The herbs infuse the sauce with a bright, aromatic note that pairs beautifully with the mushrooms.
• Spicy Kick: Add 1-2 teaspoons of red pepper flakes or a diced jalapeño along with the garlic for a subtle heat that cuts through the richness. Adjust the amount to your tolerance.
• Balsamic Glaze: After shredding, stir in 2 tablespoons of balsamic vinegar and let it simmer for 5 minutes. The vinegar brightens the sauce and adds a tangy depth that complements the pork.
• Creamy Mushroom Sauce: After shredding, stir in 1/2 cup of heavy cream or sour cream and let it warm through. This creates a richer, creamier sauce that's perfect over pasta or polenta.

Storage and make-ahead

Fridge

Store in an airtight container for up to 4 days. Reheat gently with a splash of broth or water.

Freezer

Freeze shredded pork and sauce in a freezer-safe container for up to 3 months. Thaw overnight in the fridge before reheating.

Reheat

Reheat in a skillet over medium heat, stirring occasionally, until warmed through. Add a little broth if needed to loosen the sauce.

Store any leftover shredded pork and mushrooms in an airtight container in the refrigerator for up to 4 days. The flavors will deepen as it sits. Reheat gently in a skillet or microwave, adding a splash of water or broth if the sauce has thickened too much.

This recipe is perfect for meal prep. Cook the pork a day or two ahead, shred it, and keep it in the fridge. It also freezes beautifully — see freezing instructions below.

You can also assemble the raw ingredients in the slow cooker insert the night before, cover, and refrigerate overnight. In the morning, just place the insert in the slow cooker base and turn it on.

Serving ideas

Serve the shredded pork over creamy mashed potatoes, rice, or egg noodles. The buttery mushroom sauce acts as a gravy, so spoon it generously over the top.

A side of roasted green beans or a crisp green salad balances the richness. For a low-carb option, serve over cauliflower mash or alongside sautéed spinach.

Leftovers make incredible sandwiches — pile the pork onto a soft roll, add a little of the sauce, and top with pickles or coleslaw for a pulled-pork-style treat. You can also use it as a filling for tacos or quesadillas. The possibilities are endless, and the flavor only gets better the next day.

Frequently asked questions

Recipe card

Portobello Herb Butter Pork Sirloin Roast (Slow Cooker)

Prep 10 minCook 8 hRest 5 minTotal 8 h 15 minServes 6

Ingredients

• 3 1/2 lb boneless pork sirloin roast
• 8 oz portobello mushroom caps, thickly sliced
• 2 tbsp minced garlic
• 1/2 cup salted butter (1 stick)

Instructions

1. Place the pork sirloin roast in the center of a 6-quart slow cooker. Scatter the sliced portobello mushrooms over and around the roast. Sprinkle the minced garlic evenly over the mushrooms and roast.
2. Place the whole stick of salted butter on top of the roast. It will melt as the slow cooker heats, basting the meat and mushrooms.
3. Cover the slow cooker and cook on low for 8 hours, or on high for 4-5 hours, until the pork is fork-tender and shreds easily. The internal temperature should reach at least 145°F (63°C) for safety, but cooking low and slow will take it well beyond that for fall-apart texture. Let it rest for 3 minutes before slicing.
4. Turn off the slow cooker. Using tongs, transfer the roast to a cutting board and let it rest for at least 3 minutes. Then shred the pork with two forks, discarding any large fat pieces. Return the shredded meat to the slow cooker and stir it into the buttery mushroom juices.
5. Serve the shredded pork and mushrooms over mashed potatoes or on toasted rolls, spooning extra pan juices over the top.

Contains: milk

Estimated nutrition per serving

Calories

420

Protein

38 g

Carbohydrates

4 g

Fat

28 g

Fiber

1 g

Sugar

1 g

Sodium

480 mg

Automatic estimate from the ingredient list, not laboratory-verified.