Chop the onion and add it to the pan together with 1 tbsp. butter and 1 tbsp. olive oil.
Chop the garlic and add it to the pan.
Leave until the onion is softened.
Cut the mushrooms into thin slices and add them to the pan together with the tarragon.
Wait until the mushrooms get a nice color, about 3-4 minutes.
Then put the white wine and wait for the alcohol to evaporate completely.
At the same time prepare the chicken. Put gloves and cut into 2 cm pieces.
When mushrooms are ready, remove them from the pan and leave them aside.
Pour into the same pan 1 tbsp. butter, 1 tbsp. olive oil and the chicken pieces.
Once the chicken gets a nice colour (1-2 minutes) , turn off the heat, add the brandy to the pan and let the alcohol evaporate (if we are more experienced, we can set brandy on fire.)
Add to the pan the mushrooms, the water, the heavy cream and the cube and stir smoothly.
Leave it for 5 minutes until the sauce is congealed.