Preheat the oven to 350 degrees F. then crush the pretzels. You can either pulse several times in a food processor or place them in a ziploc bag and use a rolling pin.
In a medium saucepan, melt the butter and add the 1/4 cup sugar. Stir until combined, then mix in the crushed pretzels. Press the pretzel crust evenly into a 9×13 inch casserole dish.
In a large bowl with an electric hand mixer, beat the cream cheese and powdered sugar together until smooth. Add the whipped topping last and beat until smooth.