• Preheat the oven to 400°F for 15 minutes. Time will vary depending on your oven brand. Line a half-baking sheet (18x13-inches or similar size) with parchment paper.
• Place the sugar in a small bowl. Lay the vanilla bean flat. Look for the rougher, matte side – this is where the bean naturally splits open and where you want to cut. Hold the tip of the bean down with your finger. Using the sharp tip of a paring knife, carefully cut lengthwise down the center of the bean, following the matte side. Don't cut all the way through! Leave the end intact so the bean unfolds like a book.
• Use the blunt back of the paring knife to scrape the fragrant vanilla bean seeds from the bean gently. Add the vanilla bean seeds to the sugar. Use your fingers to rub the vanilla seeds into the sugar until they are distributed throughout the sugar.
• Combine the sliced strawberries, lemon juice, and 1/2 cup of the vanilla sugar in a large bowl. With a large spoon gently mix all the ingredients together. Spread the mixture on a half-sheet pan and place in the oven.
• After the first 10 minutes, stir the berries and return the pan to the oven. Continue to roast the strawberries, stirring them every 10 minutes until the strawberry syrup starts to thicken and bubble at the edge of the pans. Total cooking time should be about 30 minutes.
• When done, remove them from the oven and immediately scrape the strawberries and juice into a large bowl using a large heatproof spatula. Be careful, the pan and the strawberry syrup are hot. You have to do this step immediately because as the syrup cools it will harden and stick to the pan.
• Allow the berries to cool until room temperature.

Storing the Strawberries

• Refrigerator: Once the strawberries are cooled to room temperature, store them in the refrigerator in an airtight container for up to 2 weeks.