One word about limes: Key limes are not the same as the 'regular' (ie: Persian/Mexican) limes you usually find at the grocery store. For one thing, they are much smaller:
Image found here.
I usually see them sold by bulk in a mesh bag instead of individually. They are much more tart than the Persian limes and lighter in color. So, to make traditional Key Lime pie you need the real thing, but it still tastes great if all you can find is Persian limes. The pie will simply not be as tart. And that neon green pie sold in stores? Not normal. I did add a couple of drops of green food coloring to my pie just for aesthetics, but it's not necessary. I just want to make sure you aren't expecting your filling to look bright green.
I really think Key Lime pie tastes best when made with a homemade graham cracker crust but I will not judge you if you use a pre-made store bought crust.
The raspberry sauce? Not a traditional topping. I got the idea from Longhorn Steakhouse - they serve(d) their Key Lime pie with a drizzle of raspberry glaze and it's a great combination. You don't have to do the same, but I thought I'd add a recipe in case you want to try it.
KEY LIME PIE
adapted from Key Lime Pie VII from Allrecipes.com
1 (9-inch) prepared graham cracker crust
2 (14 oz) cans sweetened condensed milk
1/2 cup sour cream
3/4 cup lime juice*
1 Tbsp. lime zest
green food coloring, optional
Preheat oven to 350 degrees. In a medium bowl, whisk together milk, sour cream, lime juice, lime zest, and a couple of drops of food coloring, if using; pour into prepared pie crust. Bake for 8-10 minutes or until set - do not brown. Remove to wire rack. Let cool, then refrigerate for at least 8 hours before serving.
*You will need about 10 Persian limes or 25-30 Key limes.
GRAHAM CRACKER CRUST
found on Allrecipes.com
1 1/2 cups graham cracker crumbs
1/4 cup sugar
1/3 cup butter, melted
Preheat oven to 375 degrees. In a medium bowl, combine crumbs, sugar and butter and blend well. Press into bottom and up sides of a 9-inch pie plate. Bake for 8-10 minutes. Let cool.
adapted from Allrecipes.com
1 cup fresh or frozen raspberries
2 Tbsp. sugar
1 Tbsp. orange juice
2 tsp. cornstarch
1/2 cup cold water
Combine the raspberries, sugar, and orange juice in a saucepan. In a small bowl, whisk together the cornstarch and water until smooth; add to saucepan. Bring to a boil.
Simmer for about 5 minutes, stirring constantly, until the desired consistency is reached. The sauce will thicken further as it cools.
Puree the sauce in a blender and strain through a fine mesh sieve and let cool. Sauce keeps in refrigerator up to 2 weeks.