Squash and Maple Caramelized Onion Tart - Maple from Canada

Ingredients

• 250g plain flour
• 140g unsalted butter, chilled
• 4 tbsp water
• 1 tbsp maple syrup (preferably amber for its rich taste)
• 4 tbsp extra-virgin olive oil, divided into two bowls
• 3 medium yellow onions, thinly sliced
• 3 cloves garlic, thinly sliced
• 2 tbsp Dijon mustard
• Pinch cayenne pepper
• 1 butternut squash, halved lengthwise and sliced
• 1 small, sweet potato, halved lengthwise and sliced
• 1 red onion, halved lengthwise and sliced
• 2 tbsp maple syrup (preferably golden colour for its delicate taste)
• Sea salt, to taste
• 5 sprigs thyme
• 2 tbsp unsalted butter