Lightly butter bottom and sides of a 9-in. cake pan; dust pan with flour and shake out excess.
Using a hand mixer, beat butter and sugar in a large bowl until fluffy. Add eggs one at a time to mix, beating well after each addition. Then, add in orange zest and orange extract to the butter mixture.
In another medium bowl, sift flour, baking powder and salt, then stir in cornmeal. Add dry mixture to butter mixture and beat just until blended.
Transfer the batter to the prepared pan. Place pan in oven and bake the cake until the top is golden and a toothpick inserted into center comes out with a few moist crumbs attached, about 35 minutes.
Transfer cake to a rack and cool. To remove cake from the pan, loosen edges with a knife and invert on plate or rack. Cut into wedges and garnish with orange slices.