I think the rounded tops and the problems you're having are more related to how you're mixing, and your oven temp. If the oven temp is too high, it will make the cupcakes rise too fast, then collapse. Likewise, if you've mixed too vigorously, or if thre's too much liquid in the recipe. Here's a Gale Gand recipe that's always worked for me:
YELLOW CUPCAKES – GALE GAND
cupcakes:
1 cup unsalted butter
2 cups sugar
1 1/4 teaspoons vanilla extract
4 eggs
3 cups sifted cake flour
1 tablespoon baking powder
1/2 teaspoon salt
1 cup milk
Regular or silver cupcake paper liners
Equipment: Several muffin tins
: Preheat the oven to 350 degrees F.
In a mixer with a whip attachment, cream the butter until light and fluffy. Add the sugar and continue to cream. Gradually add the vanilla and eggs and mix in well. Sift together the dry ingredients; then mix into the butter mixture alternating with the milk. Pour batter into cupcake paper-lined muffin tins filling them 3/4 full. Bake until puffed and firm in the center and light golden brown on top, about 20 to 25 minutes. Let cool. (Freeze at this point, if necessary.)
