Flour, salt and pepper in bowl; form well in centre. Gradually add milk, then water, whisking constantly until batter is smooth. Beat in eggs. Let stand 30 min.
Standard-size muffin pan in 425ºF (220ºC) oven 5 min. or until very hot. Remove from oven. Carefully spoon 1/2 tsp. (2 mL) oil into each of 72 cups (or into each of 18 cups for trial recipe). Spoon 2 Tbsp. (30 mL) batter into each cup.
15 min. or until puffed and well browned, rotating pan halfway through the baking time. Carefully remove puffs from pan; cool.
For each serving:
1/2 oz. (15 g) beef on each of 3 puffs; drizzle each with 1/2 tsp. (2 mL) bistro sauce, then garnish with a pinch of chives.