Halve kidney lengthwise; cut away most of the fat from the core. Cut into 1-inch (2.5 cm) chunks. Place in bowl and cover with cold water and a generous pinch of salt; soak for 15 minutes. Drain well; pat dry with paper towels.

In small bowl, mix cream and mustard. Trim mushroom stems so bottom of stem is flush with bottom of cap.

In skillet, melt 1 tbsp (15 mL) butter over medium-high heat; fry onion until just starting to brown, about 3 minutes. Add mushrooms; sauté until lightly browned, about 3 minutes.

Stir in 1/2 tsp (2 mL) salt; add a splash of water. Cover and reduce heat; simmer until mushrooms are tender, 5 to 6 minutes. Scrape into bowl; set aside.

Add 1 tbsp (15 mL) butter to skillet; add kidneys and 1/4 tsp (1 mL) pepper. Cook, stirring often, until kidneys are browned but still red in centre, about 5 minutes. Add brandy; bring to boil and ignite. When flames subside, add mushrooms. Bring to boil; cook for 1 minute. Reduce heat to low, stir in mustard mixture; heat through but do not boil.

Makes 4 servings.