Preheat oven to 375.

Cream the butter and sugar - cream it well, so that the butter is pale, light, and fluffy looking, about 5 minutes. Sift together the flour, salt, cinnamon and baking powder, and add to the butter and sugar mixture and and mix briefly. The mixture should be crumbly but moist enough to hold together when pressed. Set aside 1/4 cup of the mixture, and press remaining dough into tart pan, making sure the sides are strong and even. (Consider a brief pre-bake then brush bottom with melted jam.)

Add the cherries, spreading them evenly over the bottom of the pressed in dough. Sprinkle the reserved 1/4 cup of dough mixture over the cherries, carefully place the tart pan on a baking sheet (being sure not to accidentally push up on the bottom of the pan, which would dislodge your crust), and slide it into the oven. Bake for 15 minutes.

Meanwhile, whisk the eggs in a bowl, then add the half and half and whisk until it is well combined. After 15 minutes, open oven door and pull the baking sheet half way out of the oven. Carefully and quickly pour the custard mixture over the tart, then carefully and gently push the baking sheet back in, and close the oven door. Bake the tart for another 25 minutes, until the crust is a deep golden brown and the custard is set and beginning to brown.

Remove from oven and let cool slightly before removing tart ring. Let cool completely before sliding off bottom. Serve at room temperature or slightly chilled.