Preheat oven to 350°F. Spread almonds in a single layer on a baking sheet and bake for 10 minutes, taking care not to burn them. Blend in a food processor or blender until they are pulverized into small, homogenous chunks.
Whisk egg and egg yolk in a large mixing bowl until combined, then gradually add sugar, whisking as you do so. Mixture should grow paler and paler yellow, and grow shiny after about 3 minutes. Thin ribbons should form from the end of your whisk or electric beater when held about a foot above the bowl, about five minutes. Add flour and combine.
Heat milk in a medium saucepan on the stove until simmering. Add a few tablespoons to the egg mixture, and whisk to temper the milk into the eggs. Gradually add the rest of the milk, whisking as you do so. (Do not rush this process or you might end up with scrambled eggs!)
Place milk and egg mixture back in the saucepan over medium heat, whisking continuously 3-5 minutes. Remove from heat and add pulverized almonds, vanilla and almond extracts, and butter. Let cool completely, covering custard with buttered parchment paper to prevent a skin from forming.