NOTE: A HAND-HELD MIXER WORKS BEST FOR BLENDING THE FILLING, PAUSING AT INTERVALS TO SCRAPE SIDES OF MIXING BOWL. ALLOW A MINIMUM OF 4 HOURS FOR BAKED CHEESECAKE TO REFRIGERATE AND SET BEFORE SERVING. (STEP ONE): TEMPER 32 ounces Philadelphia cream cheese (four 8 ounce bricks) until room temperature is reached (about 1 1/2 hours); GRATE the outer green peel from enough key limes to yield 1/2 teaspoon plus desired amount for final garnish, using the finest shred grate of a cheese grater to produce fine zest flakes; SQUEEZE enough key limes to yield 1 cup juice.
PREHEAT oven to 375°F with one oven rack in center position and another in the lowest position; MELT 4 tablespoons unsalted butter in a microwaveable dish in a microwave for about 40 seconds for the CRUST; PROCESS enough Nilla Wafers cookies in a food processor to yield 2 cups crumbs; ADD 1 tablespoon granulated sugar; POUR butter mixture through processor feeder tube while running; PROCESS mixture until thoroughly mixed; RESERVE a few teaspoons of crumb mixture for garnish if desired; DUMP crumb mixture into a 9-inch or 10-inch springform pan; LIGHTLY spread mixture evenly into bottom of pan to approximately 1/4 inch thickness, then partway up the sides of pan.
BAKE the crust at 375°F on center rack for 5 minutes; REMOVE spring pan from oven and set aside; LEAVE oven on at 375°F.
INTO a large mixer bowl add 32 ounces tempered cream cheese, 1 1/4 cups granulated sugar, 1/4 cup flour and 1/2 teaspoon fresh Key lime zest; WHIP with mixer on medium speed until blended.
POUR in 1 cup freshly squeezed Key lime juice and 1 tablespoon pure vanilla extract while mixing on lowest speed; MIX in 1 cup real sour cream; ADD 1 (5.1 ounce) package Jell-0 Vanilla Instant Pudding mix gradually while mixing on highest speed until well blended and lump-free; BEAT 4 eggs in a separate bowl, then add to mixture, beating on lowest speed until blended, without over-mixing or creating air bubbles (pause to scrape sides of bowl if necessary).
POUR the cheesecake batter carefully into the springform pan containing crust mixture; SMOOTH mixture in swirls from edges of pan to center until level, using a flexible spatula.
BAKE cheesecake at 375°F for 15 minutes; REDUCE oven temperature to 260 F.; CONTINUE baking cheescake for 1 hour for a 10-inch pan, or 1 hour and 7 minutes, for a 9-inch pan.
REMOVE cheesecake carefully from oven; GENTLY run a sharp knife around edges of cheesecake in springform pan to loosen; LEAVE cheesecake in springform pan and allow to cool completely on a wire rack; REFRIGERATE cheesecake in the springform pan for at least 4 hours to set; REMOVE side pan carefully.
SPRINKLE a light border of cookie crumbs on cheesecake; TOP with a dollop of fresh whipped cream (use a pastry bag with decorator tip); GARNISH each serving with a pinch of finely grated fresh key lime zest and/or a fresh key lime twist if desired.