Preheat oven to 350º.
Combine pretzels, sugar and melted butter. Press into the bottom of a 9x13 pan.
Bake for 10 minutes. Set aside to cool completely.
Beat sugar and cream cheese with mixer until a smooth and creamy consistency. Mix in Cool Whip until fully combined. Spread over cooled pretzel crust. Cover crust with cream cheese mixture edge to edge, leaving no open spots (if Jell-O topping mixes with pretzels, the crust will end up soggy.) Refrigerate for 30-60 minutes.
Mix Jell-O and boiling water. Stir in frozen strawberries. Continue to stir until strawberries are thawed. Pour over cream cheese mixture (after refrigeration!) and refrigerate for another 2+ hours, until topping is set.