Prep the pan. Line the bottom of a 9-inch springform pan with parchment.
Lightly grease the sides. Wrap the outside with two layers of heavy-duty foil to protect from the water bath. Preheat oven to 325°F (163°C).
Toast the pecans. Spread all pecans on a baking sheet and toast for 7–9 minutes, until fragrant.
Cool, then finely chop 1/2 cup for the crust and roughly chop 1 cup for topping.
Make the crust. In a bowl, combine graham crumbs, 1/2 cup finely chopped pecans, 3 tablespoons sugar (taken from the granulated amount), a pinch of salt, and 6 tablespoons melted butter. Stir until the texture feels like damp sand.
Press and pre-bake. Firmly press the crust into the bottom and slightly up the sides of the pan. Bake for 10 minutes.
Let cool on a rack while you prep the filling.
Mix the filling base. In a large bowl, beat the softened cream cheese on medium speed for 2 minutes until very smooth, scraping the bowl often. Add remaining granulated sugar, cornstarch, and salt. Mix until glossy and lump-free.
Add flavor and sour cream. Beat in sour cream, maple syrup (3/4 cup), vanilla, and lemon juice if using.
Mix just until combined. The batter should be silky and slightly thick.
Add the eggs. Add eggs one at a time on low speed, mixing just to incorporate. Do not overbeat—this helps prevent cracks.
Pour and prepare the bath. Pour filling onto the cooled crust.
Place the springform pan in a large roasting pan. Pour hot water into the roasting pan to reach halfway up the springform sides.
Bake gently. Bake at 325°F for 60–70 minutes. The edges should be set, and the center should still wobble slightly when you nudge the pan.
Cool the right way. Turn off the oven, crack the door, and let the cheesecake rest inside for 45 minutes.
Remove to a rack and cool to room temperature. Then chill, uncovered, for at least 6 hours, preferably overnight.
Make the maple-pecan topping. In a small saucepan, combine 1/3 cup maple syrup, 1/4 cup brown sugar, 3 tablespoons butter, a pinch of salt, and 1/3 cup heavy cream. Simmer over medium-low heat for 3–4 minutes until glossy and slightly thickened.
Stir in the 1 cup chopped pecans. Cool until just warm.
Top and serve. Release the chilled cheesecake from the pan and remove the parchment. Spoon the warm (not hot) topping over the surface, nudging it to the edges.
Slice with a hot, clean knife. Serve chilled.