Preheat oven to 350°F. Line a 12-count muffin pan with paper liners. Set aside.
In a medium bowl, whisk flour, baking powder, and salt. Set aside.
In a large bowl, beat butter with a stand mixer or electric hand mixer on medium-high speed until smooth, about 1 minute. Add sugar and beat until light and creamy, about 3-4 minutes.
Beat in eggs, one at a time, followed by vanilla. Gradually add the flour mixture, beating on low speed, followed by milk. Beat until just combined, being careful not to overmix.
Divide the batter among the muffin cups. Bake until the tops spring back and toothpick inserted into center comes out clean, about 20-25 minutes. Remove from oven and let cool completely before frosting.
When cupcakes are cooled, fill a pastry bag (with a large tip) with jam. Insert into the top of the cupcakes and pipe in the jam.
To prepare the frosting, cream softened butter in a large bowl until light and fluffy, for about 3 minutes. Add powdered sugar, ½ cup at a time, mixing to incorporate. Add salt, milk and vanilla, beating to combine. Pipe or spread over cooled cupcakes. Top with sanding sugar, if desired.