Prep-Ahead Mashed Potatoes

3 lb. red potatoes (about 10 medium), cut into chunks
1 cup BREAKSTONE'S or KNUDSEN Sour Cream
4 oz. (1/2 of 8-oz. pkg.) PHILADELPHIA Cream Cheese, cubed
1/4 cup milk
2 Tbsp. butter
1 pkg. (8 oz.) fresh mushrooms, sliced
2 Tbsp. chopped fresh thyme
Make It

PLACE potatoes in large saucepan. Add enough water to completely cover potatoes. Bring to boil on high heat. Reduce heat to medium-low; cook 15 min. or until potatoes are tender.

DRAIN potatoes; return to saucepan. Add sour cream, cream cheese and milk. Mash with potato masher to desired consistency. Spoon into microwaveable serving bowl; cover with plastic wrap. Refrigerate up to 2 days.

MEANWHILE, melt butter in large skillet on medium-high heat. Add mushrooms; cook 5 min. or until mushrooms are tender, stirring frequently. Spoon into bowl; cover. Refrigerate until ready to use.

VENT plastic wrap covering potatoes by poking a few holes in the top just before serving. Microwave on HIGH 6 to 8 min. or until heated through; stir. Top with mushrooms. Microwave, uncovered, an additional 2 to 3 min. or until heated through. Sprinkle with thyme.