In a mixer fitted with the paddle attachment, cream the butter and sugar at medium-high speed until light and fluffy, about 2 minutes. At medium speed, add the eggs one at a time, mixing each in thoroughly before adding the next, and scraping down the sides of the bowl as needed. Beat in the lemon zest and almond extract, then raise the speed to high and beat the batter until very light, a minute or more. At low speed, mix in half of the sifted flour mixture, beating just until it is incorporated; beat in half the almond flour. Scrape the bowl, and mix in the remaining flour and almond flour. Beat briefly at medium speed to make a smooth batter. At low speed, mix in the chocolate chips just until evenly distributed. Scrape the batter into the prepared pan, and spread it in an even layer. Scatter the sliced almonds all over the top.