Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a mixing bowl, combine the flour, baking powder, and salt. Set aside.
In another bowl, cream the softened butter with the shredded cheddar and cream cheese until light and fluffy.
Gradually blend the dry ingredients into the cheese mixture until a soft dough forms.
If desired, fold in the chopped parsley for added flavor.
Roll the dough into 1-inch balls and place them on the prepared baking sheet, spacing them about 2 inches apart.
Use your thumb or the back of a spoon to make a deep indentation in the center of each ball.
Fill each indentation with hot pepper jelly.
Bake the thumbprint appetizers in the preheated oven for 20-25 minutes or until the edges are lightly golden.
Remove from the oven and allow to cool slightly before serving.