Split breast: Cut each breast in half horizontally to form 4 thin steaks in total.
Dust with flour: Sprinkle each side with salt and pepper, then sprinkle with flour and use your fingers to spread it all over the surface.
Cook chicken: Melt 15g butter in a large non-stick frying pan over medium high heat. Add chicken and cook each side for 2 ½ minutes until golden brown and just cooked through. Remove from pan, cover and keep warm.
Cook mushrooms: In the same frying pan, add remaining butter and increase heat to high. Add mushrooms and cook for 4 minutes, until starting to turn golden brown on the edges.
Add garlic later: Then add garlic and a pinch of salt and pepper, and continue cooking for another minute until both garlic and mushrooms are golden.
Deglaze skillet: Add white wine – it will bubble and be steamy! Cook for 30 seconds, scraping the bottom of the pan, until wine is mostly evaporated and the alcohol smell is gone.
Make creamy sauce: Add chicken stock, cook vigorously for 1 minute so it mostly evaporates. Then add cream, lower heat to medium and simmer for 2 minutes until it reduces and thickens slightly.
Add parmesan: Stir in parmesan, taste and add more salt and pepper if needed.
Finish chicken in sauce: Return chicken to sauce for 30 seconds (to warm through slightly.) Garnish with chives and serve as-is in the pan, for people to help themselves (or transfer to serving platter, if you prefer). Alternatively, serve a portion of chicken onto each plate, spoon sauce over and garnish with more chives.
Sides: Ideal served with mashed potato or rice – something to soak in that amazing sauce! See Note 5 for suggestions.