Make sure your baking soda totally absorb lemon juice and bubbly.
Warm up glass stovetop slightly, pour the mixture on the spot.
Put a damp kitchen towel on top.
Wait for 5 minutes, wipe off baking soda.
Use a razor blade to scape out the residue, 60 degree angle. The residue should be dark ashes left on razor.
I bought my razor blade from Wal-Mart near the car maintaining section. It turned out very useful.
Anytime I spill food or burned porridge there, I do the same thing immediately.