Preheat your oven to 350°F (175°C). Spread the pecans on a baking sheet with 1/4 cup (57g) of the butter. Toast for 8-10 minutes, stirring halfway, until fragrant. Set aside to cool. Reserve 1 cup (110g) of toasted pecans for the frosting.
Grease and flour three 9-inch round cake pans. In a large bowl with an electric mixer, or in a stand mixer, cream 1 cup (227g) of softened butter and the granulated sugar on medium-high speed until light and fluffy, about 5 minutes.
Add the eggs one at a time, mixing well after each addition. Mix in 1 teaspoon of vanilla extract.
In a separate bowl, whisk together the flour, baking powder, and salt. With the mixer on low, add one-third of the flour mixture to the butter mixture, followed by half of the milk. Repeat, ending with the last third of the flour mixture. Mix until just combined.
Gently fold in the 1 1/2 cups (165g) of toasted pecans set aside for the cake. Divide the batter evenly among the three prepared pans.
Bake for 25-30 minutes, or until a wooden skewer inserted into the center of the cakes comes out clean. Let the cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.
To make the frosting, beat the remaining 1 cup (227g) of softened butter in a large bowl until creamy. Gradually add the sifted confectioners' sugar, alternating with the evaporated milk. Beat until smooth. Mix in the remaining 1 teaspoon of vanilla.
Stir the reserved 1 cup (110g) of toasted pecans into the frosting. Once the cake layers are completely cool, place one layer on a serving plate. Spread about 1 cup of frosting on top. Repeat with the second layer. Place the third layer on top and frost the top and sides of the entire cake.