Balsamic, peppercorn steaks with homemade chips

Ingredients

• 2 tbsp balsamic vinegar
• 2 tsp concentrated liquid beef stock
• 3 garlic cloves, finely grated
• 1 tbsp wholegrain mustard
• 1 tbsp clear honey
• 2 tbsp olive oil
• 2 tsp green peppercorns, crushed
• 6 sirloin steaks, about 5cm thick
• Salad or peas, to serve (optional)
• For the chips
• 1½ kg medium potatoes, sliced finely into chips
• 3 tbsp sunflower oil, plus extra for greasing
• 1 tbsp thyme leaf