Hi Marge! Adding raspberry powder to this recipe sounds delicious. You won't want to replace any of the flour...you'll want to add the fruit powder directly to the total amount of flour in your recipe. The amount you add is truly up to you and how much flavor you want to infuse into your cake. We have found that 1/2 cup of fruit powder flavors a cake wonderfully...however, a flavor like raspberry may only take 2 to 4 Tablespoons depending on your personal taste preferences. Once you find your perfect amount, bake on! 

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