Line an 8-inch square baking pan with parchment paper.In a food processor, pulse the pretzels and gingersnaps into fine crumbs. Add the butter and pulse until the mixture holds together when pinched. Press into the bottom of the pan. Freeze 15 minutes. Scoop 4 cups vanilla ice cream out onto the frozen crust. Flatten/spread into a mostly evenly layer. Freeze 30 minutes. In a bowl, gently swirl together the strawberry ice cream and strawberry jam. Spread onto the vanilla layer. Freeze for 30 minutes more.Take a 1/2 cup of vanilla ice cream and flatten/spread onto the strawberry layer. Top with sliced strawberries. Wrap the cake and freeze 4 hours or until frozen.Remove the cake from the freezer. Use the parchment paper to lift the cake out of the pan. Let sit 5 minutes. Slice and enjoy immediately.