Preheat your oven to 325 degrees F. Spray two 8-inch cake pans with non-stick cooking spray, place a circular piece of parchment paper in the bottom of each pan, and then spray the paper. Set aside.
To a large mixing bowl, add the cake mix, eggs, milk, melted butter, and almond extract. Mix until smooth.
Divide the cake batter evenly between the two prepared cake pans. Bake for 30 minutes, or until a cake tester inserted in the center comes out clean.
Remove from the oven and let the cakes rest in the pans for 10 minutes. Run a knife along the edge and then carefully turn the cakes out onto a wire rack to cool completely. Peel the paper off the cakes once cooled and level the tops of the cakes if needed.
Filling
Add the raspberries and sugar to a medium saucepan. Place over medium-high heat and bring to a boil. Mash the berries with a fork or a potato masher.
In a small bowl, mix together the cornstarch, water, and lemon juice to make a slurry. Pour the slurry into the raspberries, return to the burner, and bring to a boil.
Cook for 1-2 minutes, stirring constantly, until the sauce is thickened and has a jam-like consistency. Remove from the heat and let cool completely.
Frosting
Add the butter and almond extract to a large mixing bowl. Beat on medium speed until fluffy, about 1 minute. Slowly add the powdered sugar, 1 cup at a time, mixing on low speed until the sugar is incorporated.
Add the heavy cream and beat on medium speed until the frosting is thick and smooth, about 2-3 minutes.
Assembly
Place a small smear of frosting in the center of the plate or cake stand you'll be using. Place the first cake layer onto the plate, bottom side down. Spread a thin layer of frosting on top of the cake to keep the sauce from seeping in.
Fill a piping bag with about 1 cup of frosting. Pipe a thick ring of frosting around the edge of the cake layer to create a barrier that'll hold the filling in. Then, using an offset spatula, spread the raspberry filling over the cake layer, being sure to keep it inside the frosting border.
Place the second cake layer on top, bottom side facing up, being sure to line it up with the edge of the first layer. Frost the top and sides of the entire cake using an offset spatula, smoothing the sides at the end.
Press almond slices into the sides of the cake. Arrange the raspberries in a ring around the top of the cake and fill in the center with more almonds. Place a few more raspberries in the center and enjoy!
Notes
Nutritional information will vary depending on how big you cut the slices of cake.
To make assembling the cake easier, pop the cake in the fridge for 15-20 minutes after frosting the bottom layer and adding the raspberry filling. Once the cake and frosting have chilled, you can add the top layer and finish frosting the cake.