Mustard pork with balsamic pears

Ingredients

• 500 grams boneless pork loin
• 1 tablespoon salt
• 2 cloves garlic, crushed
• 2 tablespoons mustard powder
• 1 teaspoon finely chopped thyme
• 1 teaspoon finely chopped rosemary
• 2 tablespoons vegetable or olive oil
• 1/4 cup balsamic vinegar
• 20 grams butter
• 1 red onion, halved, cut into wedges
• 2 pears, unpeeled, cored, stems intact, cut into wedges
• wilted spinach, to serve