Start by greasing your muffin tin thoroughly with butter or non-stick spray, ensuring all the cups and the top surface are well-coated—this prevents sticking and makes removal easier. While the oven preheats to 350°F, measure out all your ingredients and place them within arm's reach. Having everything ready before you start mixing ensures a smooth workflow and prevents the dough from sitting too long before baking.

In a large bowl, cream together the softened butter and sugar using an electric mixer on medium speed for 2-3 minutes until the mixture is light, fluffy, and pale in color. This aeration is crucial for tender cookies. Add the eggs one at a time, beating well after each addition, then add the vanilla extract and mix until fully combined. The mixture should look smooth and well-incorporated before moving to the next step.

In a separate bowl, whisk together the flour and baking powder to distribute the leavening agent evenly throughout. Add the dry ingredient mixture to the wet ingredients from Step 2, stirring gently with a spatula until just combined—don't overmix, as this can make the cookies tough. The dough should come together smoothly without any visible streaks of flour. I like to fold rather than stir at this point to keep the dough tender and light.

Using your hands or a small ice cream scoop, portion the dough into roughly 1-inch balls and place one in each greased muffin cup. Gently press each ball down slightly so it sits flat on the bottom. Using your thumb or the back of a small spoon, press down into the center of each dough ball to create a deep thumbprint—this indent is where the jam will sit, so make it substantial but don't press all the way through to the bottom.

Spoon approximately 1 tablespoon of jam into the center indent of each cookie, filling it generously but not overflowing—the jam will soften as it bakes and fill the thumbprint perfectly. Place the muffin tin into the preheated 350°F oven and bake for 13-15 minutes until the edges are golden brown and the cookies are set but still slightly tender in the centers. The jam should be bubbly and the dough should be cooked through but not dry.

Remove the muffin tin from the oven and let the cookies cool in the tin for about 5-10 minutes—this allows them to firm up enough to remove cleanly without breaking. Once slightly cooled, gently run a knife around the edges and pop each cookie out onto a wire rack to cool completely. Once fully cooled, you can dust them lightly with powdered sugar if desired for a decorative touch, though they're delicious served plain.