Chicken with creamy mushroom sauce

Name: Chicken with creamy mushroom sauce
Ingredients: 3 tbsp olive oil; 125g/4½oz unsalted butter; 4–6 boneless chicken thighs, skin on; 2 fresh thyme sprigs; 2 bay leaves; ½ bulb garlic, unpeeled, and 4 garlic cloves, chopped; 2 small onions, finely chopped; 300–400g/10½–14oz small button mushrooms; 1 bunch fresh tarragon, stalks and leaves separated, leaves chopped; 100ml/3½fl oz brandy; 250ml/9fl oz white wine; 1–2 tbsp wholegrain mustard; 1–2 tbsp Dijon mustard; 500g/1lb 2oz crème fraîche; 150g/5½oz wild garlic (or spinach); 1 bunch asparagus, tips and stalks separated (or use broccoli florets)