Buttercream Frosting

Here is the Vanilla Buttercream Frosting recipe courtesy of Southern Living March 2009.

1/2 cup butter, softened
1 tsp. vanilla extract
1/8 tsp. salt
1 (16 oz.) package powdered sugar
3 to 5 Tbsp. milk

1. Beat first 3 ingredients at medium speed with electric mixer until creamy
2. Gradually add powdered sugar alternately with 3 Tbsp. milk, 1 Tbsp. at a time, beating at low speed until blended and smooth after each addition. Beat in up to 2 Tsp. additional milk for desired consistency. Makes about 2 3/4 cups.

For Blackberry Buttercream.
Omit milk. Prepare recipe as directed in Step 1, beating in 1/2 cup fresh blackberries and 1 tsp. lemon zest with butter. Proceed with recipe as directed, beating in an additional 1 cup powdered sugar. Makes about 2 1/2 cups.

So there wouldn't be any seeds, I pureed my blackberries and sent them through a strainer, which gave me about 1/2 cup of blackberry syrup.