Mix together pretzels, butter and sugar. Spread mixture in 10x13 pan. Bake at 400°F for 8-10 minutes. Cream together sugar and cream cheese (mixture will be thick), and fold in Cool Whip. Carefully spread mixture over pretzels, and chill 30-45 minutes. Dissolve gelatin in boiling water; stir in strawberries. Cool for 30-40 minutes. Carefully pour chilled gelatin- strawberry mixture on top of cream cheese/Cool Whip layer. Chill 4-5 hours. Top with additional Cool Whip if desired.