Preheat the oven to 350 degrees F.
Butter and flour a 12-cup muffin pan, or use paper liners. In a large bowl, combine the flour baking powder, and 3/4 teaspoon salt.
In the bowl of an electric mixer, beat the sugar and butter until light and fluffy. Beat in the eggs, 1 at a time then beat in the vanilla extract. With mixer on low, beat in the flour mixture in 2 parts, alternating with milk.
Divide the batter among the prepared muffin cups. Bake until a toothpick inserted in center of a cupcake comes out clean, about 20 minutes. Let cool in the pan for 5 minutes. Remove the cupcakes from the pan and transfer to a wire rack to cool completely.
Using a paring knife, cut a 1-inch-deep piece from the top of each cupcake. Save the cut pieces. Fill each hole with 1 teaspoon of cajeta and replace the cut out pieces. Frost the cupcakes with Mexican Vanilla Buttercream Frosting.
Using an electric mixer on low speed, beat the butter and sugar until smooth. Add the salt, vanilla extract and crema. Increase the speed to high and beat until fluffy, about 3 minutes, adding extra Mexican crema, as needed, to make the frosting spreadable.
*Cajeta is a Mexican caramel sauce made from goats milk that can be found in Latin markets. If unavailable, use a rich dark caramel sauce.