Put a 9-by-5-inch loaf pan in the freezer to get cold.
Whisk the milk, egg yolks, sugar, malted milk powder and cocoa powder together in a medium bowl.
Put the chocolate chips in a large bowl.
Put the cream in a medium saucepan and heat over medium-high heat until it just starts to simmer. Slowly pour about half of the cream into the bowl with the milk/egg mixture, whisking constantly. Pour all of the liquid from the bowl back into the saucepan and cook, stirring constantly, until the custard reaches 160 degrees F, 2 to 3 minutes.
Strain the custard through a fine-mesh sieve into the bowl with the chocolate chips. Let stand 5 minutes, then stir until the chocolate is melted and thoroughly combined. Cover with plastic wrap and refrigerate until very cold, at least 4 hours.
Churn the custard in your ice cream maker according to the manufacturer's instructions. When the ice cream is ready, add the crushed malt balls and continue to churn until well distributed.
Spoon about a third of the ice cream into the cold loaf pan and spread evenly with a spatula. Drizzle in half of the chocolate syrup. Add another third of the ice cream, then smooth and drizzle with the remaining syrup. Smooth the remaining ice cream on top, then cover with plastic and freeze until firm, 2 to 3 hours.