You’ve heard me gush about “Ma’s Lemon Sponge Pie” for years. The tart and creamy lemon filling merges with an ethereal fluff that rises to the top as the pie bakes. So you’ve got the lemon curd on the bottom blending into an airy sponge cake that browns Maillard-style to add a hint of caramel. Lemon sponge pie is far better than lemon meringue pie in my book, since meringue can be wet, weepy, and have the foamy texture of something expelled by an undersea creature. A couple months ago, our friends Pam and Adam had us over for a splendid dinner of grilled delights on their rooftop patio. I brought Ma’s pie. They…