Set a clean 9 × 13-inch glass baking dish on a level surface. Measure the cold water into two portions: 1 cup for the unflavored gelatin and 1 1/4 cups for the protein powder.

Pour the 1 cup cold water into a wide heatproof mixing bowl. Sprinkle the unflavored gelatin evenly over the surface. Let it hydrate for about 5 minutes, or follow the blooming directions on your gelatin package. Avoid dumping it into one mound.

In a separate heatproof container, carefully stir the strawberry gelatin into the 2 cups freshly boiled water. Stir until the flavored powder is fully dissolved, checking the bottom for granules. Keep the container off the heat.

Pour the hot strawberry mixture over the bloomed unflavored gelatin. Whisk gently until the hydrated gelatin dissolves completely. Do not boil the combined mixture. If needed, use gentle indirect heat just long enough to dissolve remaining gelatin, then remove it from the heat.

Whisk or shake the whey powder with the remaining 1 1/4 cups cold water until smooth. Use a container that has room for mixing, and never seal hot liquid in a shaker. Let the warm gelatin mixture cool until lukewarm but still liquid. Whisk in a little of it to loosen the protein mixture, then gradually whisk the protein mixture into the gelatin bowl. Work promptly if the mixture starts to thicken.

Pour into the baking dish and skim off excess surface foam with a spoon. Cover and refrigerate on a level shelf until the entire layer is firm, allowing about 4 hours or longer as needed. Do not cut it while the center is still fluid.

Cut into a grid of 6 rows by 8 columns to make 48 cubes. Divide into eight servings of six cubes. Keep the cubes refrigerated until serving.