Make the Cremoso
In a medium heatproof bowl, lightly whisk the 5 large egg yolks and set aside.
Combine 2 cups (480 ml) of heavy cream and ⅓ cup of granulated sugar in a small saucepan.
Bring the mixture to a boil over medium heat, stirring occasionally.
Remove the cream mixture from the heat. Very slowly, pour the hot cream into the egg yolks while whisking constantly to temper the eggs and prevent scrambling.
Return the entire mixture to the saucepan.
Cook over low heat, stirring constantly, for about 1 minute, or until it has thickened enough to coat the back of a spoon.
Place the 1 pound (454 g / 16 oz) of chopped milk chocolate in a large heatproof bowl.
Pour the hot custard base over the chocolate and let it sit for a minute to melt.
Whisk the mixture until it is completely smooth and glossy.
Divide the cremoso evenly among 10 small serving bowls or cups.
Cover with plastic wrap, ensuring the wrap touches the surface to prevent a skin from forming.
Refrigerate for at least 8 hours, or overnight, until completely firm.
Prepare the Espresso Parfait
In a large mixing bowl, use a hand mixer or stand mixer to whip 2 cups (480 ml) of heavy cream, ½ cup of confectioners' sugar, and 1 teaspoon (5 ml / 0.2 fl oz) of vanilla extract until soft peaks form.
Gently fold in the 1 tablespoon (15 ml / 0.5 fl oz) of cooled espresso until just combined. Be careful not to overmix.
Spoon the parfait mixture into 10 small ramekins or a single freezer-safe container.
Freeze for at least 8 hours, or overnight, until solid.
Assemble and Serve
Just before serving, remove the cremosos from the refrigerator.
Drizzle each one with a small amount of high-quality extra-virgin olive oil and a sprinkle of flaky sea salt.
Top each cremoso with a sprinkle of the ½ cup of chopped hazelnuts.
Serve immediately with a ramekin of the frozen espresso parfait and a slice of toasted sourdough on the side for dipping.
When tempering the eggs, pour the hot cream in a very thin, steady stream while whisking vigorously. This is the key to a silky-smooth custard without any scrambled egg bits.
