Prevent sinking by adding the topping over the filling mid-way through baking. Or, increase the oven temperature by 25 degrees for the first 5 minutes to set the filling before it rises too high.u003cbr/u003eu003cbr/u003eA little more flour in the batter helps, especially if you live at a high altitude with low air pressure. The air pressure affects how your batter rises then sinks as the pumpkin streusel dessert cools.