Preheat oven to 350° Fahrenheit. Place 4 small ramekins in baking pan and set pan aside.
Add ½ cup whole milk, ½ cup heavy cream, ¼ cup granulated sugar, and ½ teaspoon pure vanilla extract to saucepan. Stir to incorporate ingredients, then place saucepan on stovetop over medium-high heat. Heat saucepan, stirring occasionally, until mixture is hot but not boiling.
While mixture comes to temperature, place 2 large egg yolks into medium heat-resistant bowl. Whisk egg yolks together until fully combined.
Once milk and sugar mixture is hot, but before mixture begins to boil, remove saucepan from heat. Slowly and carefully, pour mixture into bowl with egg yolks, whisking constantly until ingredients are fully combined and mixture is smooth and liquidy. Add mixture in increments to avoid heating eggs too quickly.
While mixture is still warm, add 5 tablespoons cookie butter and whisk vigorously until cookie butter is incorporated into custard mixture.
Fit strainer over glass measuring cup. Carefully pour cookie butter custard mixture through strainer and into measuring cup. Use back of wooden spoon to push any spices or large pieces of cookie butter through mesh of strainer.
Once custard is well strained, pour custard into ramekins, filling dishes evenly.
Carefully place baking pan holding filled ramekins in preheated oven. Before closing oven door, pour hot water directly into baking pan, being careful not to spill any water into ramekins. Add enough hot water that waterline sits halfway up outside of each ramekin.
Close oven door and bake custards 30 to 35 minutes, or until just set. To check doneness, carefully and gently wiggle ramekin. Surface of custard should jiggle uniformly around edges and in center. Surface should also look glossy and uniform in color.
Once custards are ready, carefully remove baking pan from oven and set aside. Transfer ramekins to wire cooling rack and let custards cool to room temperature. Use spoon to lightly skim any foam or bubbles off surface of custards.
Once cooled, cover each ramekin with plastic wrap. Place covered ramekins in refrigerator and let chill at least 8 hours, or place covered ramekins in freezer and let chill 30 minutes to 1 hour.