First, make the vanilla custard. Place milk in a small saucepot with vanilla. Place egg yolks, sugar, and cornstarch in a bowl and whisk together until smooth and fully incorporated. Set up an ice bath by placing ice water in a large bowl, and a separate smaller bowl to go inside. Heat the milk on medium high heat. Before it begins to boil, temper in the egg yolk mixture and return to the saucepot. Continue to whisk the custard until it’s as thick as pudding. Quickly pour custard into the bowl over ice bath, and whisk in cold butter. Continue to whisk the custard over ice water until it cools down a little. Let the custard sit in the ice bath for about 20 minutes, then divide custard into 4 ramekins (or glasses). Chill custards in refrigerator for 4+ hours, or overnight.
Preheat oven to 350 degrees Fahrenheit. To make the pistachio oat streusel, combine all ingredients in a food processor. Pulse together until it resembles small crumbles. Pour out evenly onto a sheet tray lined with parchment paper. Bake for about 8 minutes, or until golden brown. Let it cool on the sheet tray, then break it up into crumbles and set aside.
To make the roasted figs, preheat oven to 400 degrees Fahrenheit. Quarter all figs and toss them into a bowl with the remaining ingredients. Spray a 9x13 inch baking dish with non-stick baking spray, then pour in fig mixture. Roast on the top rack of your oven for about 15 minutes. Figs should look like they’ve broken down and there should still be some sauce pooled around. Transfer figs and juices to a small bowl and prepare to assemble.
To assemble the parfaits, scoop pistachio streusel over the custard, and top with roasted figs. Continue for each parfait, and serve immediately. Enjoy!