As explained in Fantastic Foods With Splenda by Marlene Koch, perhaps your biscotti did not turn out because, in baking, sugar not only provides sweetness but also texture, color, etc. So, when removing sugar and using Splenda, you need to increase the fat to compensate. The following is from the cookbook...

CREAMY LEMON BARS
Source: Fantastic Foods With Splenda by Marlene Koch

CRUST:
1 cup all-purpose flour
1/3 cup Splenda Granular
1/2 tsp. lemon zest
4 Tbsp. margarine or butter
2 Tbsp. light cream cheese
TOPPING:
2 large eggs + 2 egg whites
6 Tbsp. lemon juice
1 cup Splenda Granular
1 1/2 Tbsp. light corn syrup
1 Tbsp. all-purpose flour
1 1/2 lemon zest
1/2 tsp. baking powder
2 tsp. powdered sugar (OPTIONAL)

TO PREPARE THE CRUST:
Preheat oven to 375 degrees F. Spray an 8-inch square pan with nonstick baking spray.

In a medium bowl mix together flour, Splenda, and lemon zest. Cut in margarine or butter. Mix in cream cheese until you have fine crumbs. Press onto the bottom of the prepared pan.

Bake for 15 minutes.

WHILE CRUST IS BAKING, PREPARE TOPPING:
In a large bowl beat the eggs and egg whites with the lemon juice, Splenda, and corn syrup until frothy. Briefly beat in flour, zest, and baking powder. Pour over hot baked crust.

Turn down to 350 degrees F and bake bars additional 18-20 minutes or until top is set. Cool completely.

Just prior to serving, dust with powdered sugar if desired

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ZEBRA BARS
Source: Fantastic Foods With Splenda by Marlene Koch

1 oz. semisweet chocolate
2 Tbsp. margarine
1/4 cup pune puree or 1-2.5oz. jar babyfood prunes
3 Tbsp. brown sugar
2/3 cup Splenda Granular
1/4 cup cocoa powder
1 large egg + 2 egg whites
1 1/2 tsp. vanilla
1 Tbsp. hot tap water
3/4 cup all-purpose flour
1/2 tsp. baking powder
1/4 tsp. baking soda
1/2 cup cream cheese, light tub-style
2 Tbsp. egg white (reserved)
2 Tbsp. Splenda Granular
1 Tbsp. powdered sugar
1/2 tsp. vanilla

Preheat oven to 325 degrees F. Spray a 7x11 or 9x9-inch baking pan with nonstick cooking spray.

Melt chocolate and margarine together in medium bowl by microwaving on high for 30-60 seconds. Whisk in next 8 ingredients (reserving 2 Tbsp. of egg white). Blend until smooth.

Sift in flour, baking powder, and baking soda. Mix just until flour is incorporated and pour batter into prepared baking pan.

In a small bowl beat together last 5 ingredients. Drop by teaspoonfuls onto top of chocolate batter. Pull knife through batter to create swirl pattern.

Bake 20-22 minutes; just until center feels firm to touch.

Cathy, I hope these are something that you can use. If you try them, please let us know how they turned out because there are several friends on this site that are using Splenda. If you are looking for a specific/favorite cookie let us know that too and we can try to find a Splenda alternative. Also, if you need the Diabetic exchange, WW point comparison or calorie content of the above I can provide that.