Prepare the ramekins. Preheat an oven to 300°F (150°C) with a rack in the center position. Place 4 ramekins in a 9x9 baking pan. Bring a large kettle of water to a boil.
Warm the cream mixture. Combine 2 cups (475ml) heavy cream, ¼ cup (50g) granulated sugar, and a pinch of Kosher salt in a medium saucepan, then set over medium heat. Cook, stirring occasionally, until the sugar has dissolved.
Mix in the egg yolks. Place 5 room temperature egg yolks in a large mixing bowl, then whisk. Slowly add the warmed cream mixture a little at a time, whisking constantly, until the cream is fully incorporated into the egg yolks.
Add espresso powder. In a separate small bowl, whisk together 1 Tbsp instant espresso powder with 1 Tbsp Kahlua until dissolved. Stir into the cream mixture, then strain through a fine mesh sieve set over a large measuring cup or bowl with a spout.
Bake the custards. Divide the mixture evenly between the four ramekins. Pour enough hot water into the baking dish so that it reaches at least half way up the sides of the ramekins. Carefully place in an oven and bake for 25-35 (40-45) minutes, or until the custards are just set. To check if they’re done, give the baking dish a little shake – only the centers of the custard should jiggle slightly. (Note: Times may vary based on the depth of the remkin used).
Refrigerate until needed. Carefully transfer the custards to a wire rack to cool completely, about 4 hours. Cover each with plastic wrap, then refrigerate for at least a few hours, or until needed. Can be made ahead at this point 2 days in advance.
Brulée the top. When ready to serve, evenly sprinkle 1 Tbsp of sugar on top of each custard, rotating the ramekin as needed to cover as much surface area as possible. Use a kitchen torch to melt the sugar, which will then bead and solidify. Continue with the blow torch until the sugar caramelizes, turns golden brown, and forms a hard crust. Serve immediately!